Submodules and how to update

UPP is a submodule of WAFS, and GTG is submodule of UPP:
WAFS --> UPP --> GTG

How to update the UPP submodule:

1. Edit .gitmodules, change branch to the right tag/branch of UPP
2. Follow the following steps:

git remote add upstream git@github.com:NOAA-EMC/WAFS.git
git clone git@github.com:YaliMao-NOAA/WAFS.git wafs.fork
cd wafs.fork
git fetch upstream
git checkout upstream/develop
git switch -c forGFSv17

sh sorc/checkout_upp.sh
cd sorc/wafs_upp.fd
git remote update
git checkout develop 
cd  ../../

git commit -am "update UPP code revision"
git push origin yourbranch