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 ## What It Does
 
-TK: what problem does this solve, and how?
+**The problem:** The personal task manager application [Things](https://culturedcode.com/things/) does not support attaching files/images to tasks. This is one of my main complaints about the app compared to eg. [OmniFocus](https://www.omnigroup.com/omnifocus/).
+
+**The solution:** `mailto-things` will:
+1. Check for incoming emails in a Gmail account
+2. Strip out the attachments from each email and put the files in a directory tree on disk
+3. Replace the attachments in the email by URLs linking to the attachment files
+4. Send the modified email along to Things via [the app's "Mail to Things" feature](https://culturedcode.com/things/support/articles/2908262/)
+
+The end result is that you can email files to your specially-configured email address, and the resulting tasks in your Things inbox contain links to those files. This is as close as I can get to actually attaching files directly to things.
 
 ## Installation
 
-TODO(cdzombak): make install target
+To install the binary on your server, clone this repository and run `make install`. If you prefer to build the program elsewhere, the Makefile provides some targets for cross-compilation, eg. `make build-linux-amd64`. Run `make help` for a list of targets. The build products are placed in `./out`; just copy the `mailto-things` binary to wherever you want to run it.
+
+### Web Hosting
+
+Attachment files must be written to a web-accessible directory. This is beyond the scope of this README, but basically you just need a writable folder which the web server can read & serve from. I strongly recommend disabling directory listing on that folder!
+
+I'm placing attachment files in my [public "Dropbox" folder](https://www.dzombak.com/blog/2014/01/serving-dropbox-via-nginx.html), though I now use [Syncthing](https://syncthing.net) instead of Dropbox for sharing stuff between my computers & servers. This means that, in addition to my attachment files being web-accessible, they're synchronized locally to my computers for offline use.
+
+### Gmail App Credentials
 
-TK: install docs
+You will need to create a Google Cloud Platform project with access to the Gmail API. The easiest way to do that is Step 1 on Google's [Gmail API Go Quickstart](https://developers.google.com/gmail/api/quickstart/go) documentation page. Download the resulting `credentials.json` file and store it in a private `mailto-things` configuration directory on the server you'll use to run this program.
 
-## Usage
+## Usage & Configuration
 
-TK: how do you run this?
+Note that the first time you run the program you'll have to authorize its access to your Gmail account. Therefore, test your configuration by running `mailto-things` in an interactive shell before setting up a cronjob.
+
+All of the following arguments (or their equivalent environment variables) are required:
+
+- `-configDir`: Path to the directory where `credentials.json` & user authorization tokens are stored. (Overrides environment variable `MAILTO_THINGS_CONFIG_DIR`.)
+- `-attachmentsDir`: Path to the directory on disk where attachments are stored. (Overrides environment variable `MAILTO_THINGS_ATTACHMENTS_DIR`.)
+- `-attachmentsDirURL`: URL to the directory where attachments are stored. Should not end with a slash. (Overrides environment variable `MAILTO_THINGS_ATTACHMENTS_DIR_URL`.)
+- `-incomingEmail`: Email address which receives tasks with attachments. This is your new "Things Inbox" email address, to which you will send messages. (Overrides environment variable `MAILTO_THINGS_INCOMING_EMAIL`.)
+- `-outgoingEmail`: [Mail to Things](https://culturedcode.com/things/support/articles/2908262/) email address to send task emails to. (Overrides environment variable `MAILTO_THINGS_OUTGOING_EMAIL`.)
+
+The following arguments are not strictly required, but you will almost definitely need to set them:
+
+- `-fileCreateMode`: Octal value specifying the [permissions](https://web.archive.org/web/20201207170802/https://www.grymoire.com/Unix/Permissions.html) used to create file attachments on disk. Must begin with `0` or `0o`. Defaults to `0600`.
+- `-dirCreateMode`: Octal value specifying the [permissions](https://web.archive.org/web/20201207170802/https://www.grymoire.com/Unix/Permissions.html) used to create attachment directories on disk. Must begin with `0` or `0o`. Defaults to `0700`.
+
+Additionally, `-version` will print the version number and exit.
 
 ### Cron Example
 
+Here's an example of running `mailto-things` periodically via cron, adapted from my own usage:
+
 `
-*/5		*	*	*	*	runner -print-if-match "could not parse message part" -work-dir /home/cdzombak/mailto-things -- ./mailto-things -configDir /home/cdzombak/mailto-things -attachmentsDir /home/cdzombak/Sync/public/mailto-things -attachmentsDirURL "https://dropbox.dzombak.com/mailto-things" -fileCreateMode 0644 -dirCreateMode 0755 -incomingEmail "example+things@gmail.com" -outgoingEmail "add-to-things-example@things.email"
+*/5		*	*	*	*	runner -print-if-match "could not parse message part" -work-dir /home/cdzombak/mailto-things -- ./mailto-things -configDir /home/cdzombak/mailto-things -attachmentsDir /home/cdzombak/Sync/public/mailto-things -attachmentsDirURL "https://dropbox.dzombak.com/mailto-things" -fileCreateMode 0644 -dirCreateMode 0755 -incomingEmail "example+mailtothings@gmail.com" -outgoingEmail "add-to-things-example@things.email"
 `
 
-TK: link to runner / blog post
+This example uses my [`runner` tool](https://github.com/cdzombak/runner) ([introductory blog post](https://www.dzombak.com/blog/2020/12/Introducing-Runner--a-lightweight-wrapper-for-cron-jobs.html)) to avoid emailing me output unless something went wrong.
 
 ## About