docs: Release checklist (#999)

Co-authored-by: Erik Svedang <erik@Eriks-iMac.local>

docs/ReleaseChecklist.md

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+# Release Checklist
+
+Do all of these things (somewhat) in order:
+
+# 1. Update Cabal project version
+
+See the second line of the file [CarpHask.cabal](../CarpHask.cabal).
+
+# 2. Update the "Welcome to Carp X.Y.Z" REPL message
+
+See [Main.hs](../App/Main.hs).
+
+# 3. Make a commit on master
+
+```bash
+$ git commit -m "Release X.Y.Z"
+```
+
+# 4. Tag the commit and push it
+
+```bash
+$ git tag vX.Y.Z
+$ git push --tags
+```
+
+# 5. Update the blurb in README.md
+
+See [README.md](../README.md)