Add release steps.

MAINTAINING.md

+# Maintaining
+
+## Releasing a new version
+
+This project follows [semver](http://semver.org/). So if you are making a bug
+fix, only increment the patch level "1.0.x". If any new files are added, a
+minor version "1.x.x" bump is in order.
+
+### Make a release commit
+
+To prepare the release commit:
+
+1. Edit the [bower.json](https://github.com/github/fetch/blob/master/bower.json)
+`version` value.
+2. Change the npm [package.json](https://github.com/github/fetch/blob/master/package.json)
+`version` value to match.
+3. Make a single commit with the description as "Fetch 1.x.x".
+4. Finally, tag the commit with `v1.x.x`.
+
+```
+$ git pull
+$ vim bower.json
+$ vim package.json
+$ git add bower.json package.json
+$ git ci -m "Fetch 1.x.x"
+$ git tag v1.x.x
+$ git push
+$ git push --tags
+```