Add guide for release

devtool/release_new_version.md

@@ -0,0 +1,11 @@
+# Steps to release a new version 
+
+- Change the version by modifying `major`, `minor` and `patch` in `./update_version.py` 
+  and then `$ python update_version.py`
+- Format code `$ python format_sources.py`
+- Update docs at `kliff/docs/source` as necessary 
+- Update `kliff/docs/source/changelog.rst`
+- Generate docs by running `$ make html` in the `kliff/docs` directory
+- Commit and merge it to the `docs` branch. [ReadTheDocs](https://readthedocs.org) 
+  is set up to watch this branch and will automatically generate the docs.)
+- Go to GitHub and release a new version by tagging it with `v<major><minor><patch>`