Update CONTRIBUTING: add cmd to push tags (google#1082)

CONTRIBUTING.md

@@ -57,19 +57,15 @@ repo.
     git tag dependencies/$REL
     ```
 
-7.  Push the new tags to the main repo (which is named `upstream` in my setup)
-    either one by one or all together provided you have no other new tags
-    defined. The following illustrates the latter, and does a dry run first:
+7.  Push the new tags to the main repo (which is named `upstream` in my setup):
 
     ```console
-    $ git push --dry-run --tags upstream
-    To https://github.com/google/docsy.git
-    * [new tag]         dependencies/v0.X.Y -> dependencies/v0.X.Y
+    $ git push upstream $REL && git push upstream dependencies/$REL
+    ...
     * [new tag]         v0.X.Y -> v0.X.Y
+    * [new tag]         dependencies/v0.X.Y -> dependencies/v0.X.Y
     ```
 
-    If only the two new tags are listed, drop the dry-run flag to push the tags.
-
 8.  Use the GitHub [Draft a new release][] feature, filling in the fields as
     follows:
 
@@ -89,8 +85,8 @@ repo.
 
     -   Replace the `0XY` anchor target above with a target appropriate for this
         release.
-    -   Remove the "New contributors" autogenerated text since we don't publish
-        that as part of our release notes.
+    -   Remove the "New contributors" autogenerated text (if present) since we
+        don't publish that as part of our release notes.
     -   Select **Create a discussion for this release**.
     -   Click **Publish release**.