Pkg has noticed that your local git repository is not ready to create a pull request.
Best practice is to create a feature branch before you make any changes.
git checkout master
git checkout -b yourfeaturebranch
Then make your changes, including adding relevant test cases in to test/runtests.jl, and ensure the tests all pass. Then commit our changes before running Pkg.submit("PackageName") again.
git add .
git commit -m "useful commit message"
If you have already made changes, the workflow is slightly different.
git checkout -b yourfeaturebranch
git rebase -i origin/master
git add .
git commit -m "useful commit message"
Once you have submitted your pull request, you may be asked to make further modifications before it is accepted. Pkg.submit() has configured your branch such that push XXX YYY will push any new commits to yourfeaturebranch to the pull request.