CHG: More clarification about HTTPS vs SSH

README.md

@@ -11,10 +11,18 @@ ISSM is a large-scale thermo-mechanical 2D/3D parallelized multi-purpose finite-
  - Website:	https://issm.jpl.nasa.gov
 
 ## Checking Out a Copy of the Repository
-Navigate to the parent directory where you want the ISSM repository to be located and run,
+Navigate to the parent directory where you want the ISSM repository to be located. If you plan to make contributions to the code base, we recommend that you check out a copy via SSH with,
 ```
 git clone [email protected]:ISSMteam/ISSM.git
 ```
+Note that you will you first need to <a href="https://docs.github.com/en/authentication/connecting-to-github-with-ssh/adding-a-new-ssh-key-to-your-github-account" target="_blank">add an SSH key to your GitHub account</a>.
+
+If you plan only to use ISSM without making contributions, you also have the option of checking out a copy via HTTPS.
+
+```
+git clone https://github.com/ISSMteam/ISSM.git
+```
+Note that checkout via HTTPS does not require credentials, but does not allow commits without first setting up a personal access token.
 
 ## Committing Changes to the Repository
 A good basic workflow for committing changes to the repository is,
@@ -45,12 +53,17 @@ git push
 
 6. Submit a pull request via GitHub so that project admins can review your changes and merge them into the main branch.
 
+If you find yourself making a lot of commits and pull requests, consider asking us to add you to the 'ISSM Contributors' group, which will allow you to make commits directly to the repository.
+
 ## Troubleshooting
-### fatal: unable to access 'https://github.com/ISSMteam/ISSM.git/': The requested URL returned error: 403
-If you get this error on commit to the repository, it means you originally cloned via HTTPS. To fix this, switch to the SSH protocol with,
+### fatal: unable to access 'https[]()://github.com/ISSMteam/ISSM.git/': The requested URL returned error: 403
+If you get this error on commit to the repository, it means you originally cloned via HTTPS. You have two options here,
+1. <a href="https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/managing-your-personal-access-tokens" target="_blank">Create a personal access token</a> and use it in place of your password when prompted for credentials.
+2. Change the config for this clone of the repository to use the SSH protocol with,
 ````
 git remote set-url origin [email protected]:ISSMteam/ISSM.git
 ````
+Note that in the second case you will have to create an SSH key and add it to your GitHub account.
 
 ## Resources
  - Git Guides: https://github.com/git-guides