Does not check that README.md exists during checks.

[rupertlssmith]

If you have not yet created the release tag and run 'elm-package publish', it suggests the git commands to run to create the tag.

Once the tag is created, running 'elm-package publish' again can fail, if a file called 'README.md' is not present. It also fails on 'Readme.md'.

This is a bit annoying and may lead to having to delete the tag, rename and re-tag. Checking that 'README.md' is present during the checking and suggesting phase would be very helpful.

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.