docs(CONTRIBUTING): add note about how type definitions and API docs are generated and published automatically

Author: gr2m

CONTRIBUTING.md

@@ -44,4 +44,7 @@ Only one version number is bumped at a time, the highest version change trumps t
 Besides publishing a new version to npm, semantic-release also creates a git tag and release
 on GitHub, generates changelogs from the commit messages and puts them into the release notes.
 
+Before the publish it runs the `npm run build` script which generates type definitions for Flow & Typescript based on the [templates](scripts/templates/).
+The script also generates the API docs. After the publish, the API docs are automatically pushed to the `gh-pages` branch which updates the documentation at  [octokit.github.io/node-github](http://octokit.github.io/node-github/).
+
 If the pull request looks good but does not follow the commit conventions, use the "Squash & merge" button.