Release v0.6.0 (#269)

It's been quite a while! Let's cut a release. I also added some docs
with a checklist, although it's mostly not very interesting.

Test plan: read recent issues

docs/CHANGELOG.md

@@ -22,6 +22,14 @@ When releasing a new version:
 
 ### Breaking changes:
 
+### New features:
+
+### Bug fixes:
+
+## v0.6.0
+
+### Breaking changes:
+
 - genqlient now requires Go 1.18 or higher.
 
 ### New features:

docs/CONTRIBUTING.md

@@ -45,3 +45,14 @@ If you update any code-generation logic or templates, even if no new tests are n
 ## Finding your way around
 
 If you're new to genqlient, start out by reading the source of `generate.Generate`, whose comments describe most of the high-level operation of genqlient.  In general, the code is documented inline, often with an introductory comment at the top of the file.  See [DESIGN.md](DESIGN.md) for documentation of major design decisions, which is a good way to get a sense of why genqlient is structured the way it is.
+
+## Making a release
+
+We try to cut releases periodically. To make a release:
+
+- Scan PRs since the last release to check we didn't miss anything in the changelog.
+- Check if there are any regressions or major problems with new features we want to fix before cutting the release.
+- Decide the new version number. We do a minor version bump for anything with breaking changes or significant new features, otherwise it can be a patch version bump.
+- Add a new section to the changelog (see comments in the changelog for instructions).
+- Make a PR with the above. (Example: [#208](https://github.com/Khan/genqlient/pull/208).)
+- When it merges, tag it as the new release, e.g. `git checkout main && git pull && git tag v0.X.Y && git push origin v0.X.Y`.