chore: freeze 0.13.0 (#487)

* chore: freeze 0.13.0

* add release process doc

Author: nyobe

.version

@@ -1 +1 @@
-0.12.0
+0.13.0

CHANGELOG.md

@@ -1,6 +1,20 @@
 CHANGELOG
 =========
 
+## 0.13.0
+
+### Improvements
+
+- Add `--string` flag to `env set` to treat the given value as a string.
+  [#467](https://github.com/pulumi/esc/pull/467)
+- Add proper return code to list environments when organization doesn't exist
+  [#484](https://github.com/pulumi/esc/pull/484)
+
+### Breaking changes
+
+- It is now a syntax error to call a builtin function incorrectly.
+  [449](https://github.com/pulumi/esc/pull/449)
+
 ## 0.12.0
 
 ### Improvements

CONTRIBUTING.md

@@ -0,0 +1,8 @@
+## Performing a release
+
+We use [goreleaser](https://goreleaser.com/intro/) for automating releases. 
+To cut a new release, create a commit that:
+- Copy the entries in [CHANGELOG_PENDING](./CHANGELOG_PENDING.md) into [CHANGELOG](./CHANGELOG.md). 
+  CHANGELOG_PENDING is used to generate the release notes. After releasing, the following commit can clear the changes from pending.
+- Bumps the version in the [.version](./.version) file, which is used to stamp the version into the binary.
+- Tag the commit with a version tag in the format vX.X.X, to trigger the [release automation](./.github/workflows/publish-release.yaml).