Update section about submitting patches in README

Try to cover the most common reasons for requesting changes in PRs.

README.md

@@ -231,15 +231,33 @@ saw never get modified.
 Submitting Patches
 ------------------
 
-Please use the [issue-tracker](https://github.com/frej/fast-export) at
-github to report bugs and submit patches.
+Please create a pull request at
+[Github](https://github.com/frej/fast-export/pulls) to submit patches.
+
+When submitting a patch make sure the commits in your pull request:
+
+* Have good commit messages
+
+  Please read Chris Beams' blog post [How to Write a Git Commit
+  Message](https://chris.beams.io/posts/git-commit/) on how to write a
+  good commit message. Although the article recommends at most 50
+  characters for the subject, up to 72 characters are frequently
+  accepted for fast-export.
+
+* Adhere to good [commit
+hygiene](http://www.ericbmerritt.com/2011/09/21/commit-hygiene-and-git.html)
+
+  When developing a pull request for hg-fast-export, base your work on
+  the current `master` branch and rebase your work if it no longer can
+  be merged into the current `master` without conflicts. Never merge
+  `master` into your development branch, rebase if your work needs
+  updates from `master`.
+
+  When a pull request is modified due to review feedback, please
+  incorporate the changes into the proper commit. A good reference on
+  how to modify history is in the [Pro Git book, Section
+  7.6](https://git-scm.com/book/en/v2/Git-Tools-Rewriting-History).
 
-Please read
-[https://chris.beams.io/posts/git-commit/](https://chris.beams.io/posts/git-commit/)
-on how to write a good commit message before submitting a pull request
-for review. Although the article recommends at most 50 characters for
-the subject, up to 72 characters are frequently accepted for
-fast-export.
 
 Frequent Problems
 =================