Contributing section in readme

Author: ezolenko

README.md

@@ -199,3 +199,19 @@ Check if you get the same problem with `clean` option set to true (might indicat
 If makes sense, check if running `tsc` directly produces similar results.
 
 Attach plugin output with `verbosity` option set to 3 (this will list all files being transpiled and their imports).
+
+### Contributing
+
+Use the normal github process of forking, making a branch and creating a PR when ready. Fix all linting problems (run `npm lint`), fix any failed checks that are run on the PR (basically lint right now). Use an editor that supports editorconfig, or match the settings from `.editorconfig` file manually.
+
+Fastest way to test changes is to do a self build, the plugin is part of its own build system:
+- make changes
+- run `npm build` (uses build committed to master branch)
+- check that you get expected changes in `dist`
+- run `npm build-self` (uses fresh local build)
+- check `dist` for the expected changes
+- run `npm build-self` _again_ to make sure plugin built by new version can still build itself
+
+If `build-self` breaks at some point, fix the problem and restart from `build` step (a known good copy).
+
+This repo badly needs unittests though.