Documentation tweaks relating to releases (#271)

A few tweaks I noticed after doing this release:
- I forgot to add a summary line to this release; and forgot to mention
this in the release documentation.
- Steve suggested we create GitHub releases, so I added his instructions
for doing that.
- An older documentation link was wrong.

docs/CHANGELOG.md

@@ -30,6 +30,8 @@ When releasing a new version:
 
 ## v0.6.0
 
+Version 0.6.0 includes some small features and bugfixes. Note that genqlient now requires Go 1.18 or higher, and is tested through Go 1.20.
+
 ### Breaking changes:
 
 - genqlient now requires Go 1.18 or higher.
@@ -80,7 +82,7 @@ Version 0.4.0 adds several new configuration options, as well as additional meth
 ### New features:
 
 - genqlient now generates getter methods for all fields, even those which do not implement a genqlient-generated interface; this can be useful for callers who wish to define their own interface and have several unrelated genqlient types which have the same fields implement it.
-- The new `struct_references` option automatically sets the `pointer` and `omitempty` options on fields of struct type; see the [`genqlient.yaml` documentation](docs/genqlient.yaml) for details.
+- The new `struct_references` option automatically sets the `pointer` and `omitempty` options on fields of struct type; see the [`genqlient.yaml` documentation](genqlient.yaml) for details.
 - genqlient config now accepts either a single or multiple files (or globs) for the `schema` and `operations` fields (previously it accepted only one `schema`, and required a list of `operations` files).
 - genqlient now looks for its config file as `[.]genqlient.y[a]ml` in any ancestor directory, if unspecified, rather than only as `genqlient.yaml` in the current directory.
 - The `typename` option can now be used on basic types (string, int, etc) as well as structs; this can be useful to have genqlient define new types like `type Language string` and use that type for specified fields.