Add GBM PR body template

cli/templates/release/gbm_pr_body.md

@@ -0,0 +1,27 @@
+Release for Gutenberg Mobile {{ .Version }}
+
+<!-- ## Related PRs
+{{ range .RelatedPRs }}
+- {{ .Url }}{{ end }}
+
+## Changes
+
+{{ range .Changes }}
+### {{ .Title }}
+* PR {{ .PrUrl }}
+{{ range $i, $issue := .Issues }}
+* Issue {{ $i }}{{ $issue }}{{ end }}
+{{ end }} -->
+
+
+<!-- To determine the changes you can check the RELEASE-NOTES.txt and gutenberg/packages/react-native-editor/CHANGELOG.md files and cross check with the list of commits that are part of the PR -->
+## Test plan
+
+Once the installable builds of the main apps are ready, perform a quick smoke test of the editor on both iOS and Android to verify it launches without crashing. We will perform additional testing after the main apps cut their releases.
+
+## Release Submission Checklist
+
+- [ ] Verify Items from test plan have been completed
+- [ ] Check if `RELEASE-NOTES.txt` is updated with all the changes that made it to the release. Replace `Unreleased` section with the release version and create a new `Unreleased` section.
+- [ ] Check if `gutenberg/packages/react-native-editor/CHANGELOG.md` is updated with all the changes that made it to the release. Replace `## Unreleased` with the release version and create a new `## Unreleased`.
+- [ ] Bundle package of the release is updated.