Add release instructions. Fixes #29.

.bumpversion.cfg

@@ -0,0 +1,6 @@
+[bumpversion]
+current_version = 0.3
+commit = True
+tag = True
+
+[bumpversion:file:pep517/__init__.py]

RELEASE.rst

@@ -0,0 +1,9 @@
+To cut a release, use
+`bump2version <https://github.com/c4urself/bump2version>`_,
+the `preferred version
+<https://github.com/peritus/bumpversion/pull/58#issuecomment-428956095>`_
+of bumpversion. Something like:
+
+    bump2version minor
+
+Then push the commit and tags to GitHub.