docs: Update release docs for versioned formula (argoproj#2245)

Signed-off-by: zachaller <[email protected]>

docs/releasing.md

@@ -24,8 +24,20 @@
     ```bash
     cd homebrew-tap
     ./update.sh kubectl-argo-rollouts $VERSION
-    git commit -am "Update kubectl-argo-rollouts to $VERSION"
     ```
+   * If there is a new minor version we want to update the versioned formula as well:
+     * Run the following commands to update the versioned brew formula:
+          ```bash
+          ./update.sh kubectl-argo-rollouts $VERSION @<version_without_patch_and_v>
+          ```
+     * Example: If the new version is `v1.3.2`, we want to update the formula for `v1.3` as well.
+         ```bash
+         ./update.sh kubectl-argo-rollouts v1.3.2 @1.3
+         ```
+   * Commit and push the changes to your fork
+     ```bash
+     git commit -am "Update kubectl-argo-rollouts to $VERSION"
+     ```
    * Create a PR with the modified files pointing to upstream/master
    * Once the PR is approved by a maintainer, it can be merged.