Add config for goreleaser, document release process

Release.md

@@ -0,0 +1,33 @@
+1. Export `$VERSION`:
+
+      export VERSION=0.10.0
+
+2. Add new version to file VERSION:
+
+      echo "${VERSION}" | tee VERSION && git commit -m "Update VERSION file for ${VERSION}" VERSION
+
+3. Move changelog files for `calens`:
+
+      mv changelog/unreleased "changelog/${VERSION}_$(date +%Y-%m-%d)"
+      git add "changelog/${VERSION}"*
+      git rm -r changelog/unreleased
+      git commit -m "Move changelog files for ${VERSION}" changelog/{unreleased,"${VERSION}"*}
+
+4. Generate changelog:
+
+      calens > CHANGELOG.md
+      git add CHANGELOG.md
+      git commit -m "Generate CHANGELOG.md for ${VERSION}" CHANGELOG.md
+
+5. Tag new version and push the tag:
+
+      git tag -a -s -m "v${VERSION}" "v${VERSION}"
+      git push --tags
+
+6. Build the project (use `--skip-publish` for testing):
+
+      goreleaser \
+        release \
+        --config ../.goreleaser.yml \
+        --release-notes <(calens --template changelog/CHANGELOG-GitHub.tmpl --version "${VERSION}")
+