releases: break up first git tag for verification purposes

I'm not sure what went wrong, but the first RC I cut had some trouble
with the tag being picked up with `git describe`, I think it was missing
a 'tag message'. I'm not sure what caused this.

This commit breaks up the first git tag procedure to have the releaser
verify that the tag command works as intended (and sensitizes them to
checking this for subsequent release cuts, if necessary)

doc/MAKING-RELEASES.md

@@ -29,8 +29,11 @@ Here's a checklist for the release process.
 
 ### Releasing -rc1
 
-1. Merge the PR above.
+1. Merge the above PR.
-2. Tag it `git pull && git tag -s v<VERSION>rc1 && git push --tags`
+2. Tag it `git pull && git tag -s v<VERSION>rc1`. Note that you
+   should get a prompt to give this tag a 'message'. Make sure you fill this in.
+3. Confirm that the tag will show up for builds with `git describe`
+4. Push the tag to remote `git push --tags`.
 3. Update the /topic on #c-lightning on Freenode.
 4. Prepare draft release notes (see devtools/credit), and share with team for editing.
 5. Upgrade your personal nodes to the rc1, to help testing.