By the way, you don’t need to wait for merge from the project owner. For example, you may test my unmerged PR 222 for nested Staticman comment support by the following commands.
$ git remote -v
upstream https://github.com/halogenica/beautifulhugo.git (fetch)
upstream https://github.com/halogenica/beautifulhugo.git (push)
... # other remote omitted
$ git checkout -b pr222 # test on a new branch pr222
$ git fetch upstream pull/222/head # git pull will be rejected
$ git merge FETCH_HEAD # manually merge the this PR against branch pr222
$ cd <your-blog>
... # edit your .gitmodules with url="<repo-containing-pr222>" and branch = "pr222"
$ git submodule sync # inform Git the changes in .gitmodules
$ git submodule update --remote --recursive # switch to the HEAD of your cloned repo for the theme