You'd probably want to have a script that does a 'git pull' inside each cloned repo directory. I'm assuming you're on windows- here's a pretty basic batch script you could use:
(Note the path to git bin folder on line 2. You won't need that line if git is already in your PATH. You can open up a command prompt and type in 'git', and see if it recognizes it.)
ECHO OFF
set PATH=%PATH%;"C:\Program Files (x86)\Git\bin"
cd D:\SteamCMD\garrysmod\garrysmod\addons\
cd Ulysses
git pull
cd ..
cd cooladdonyeah
git pull
cd ..
pause
Obviously, you'll have to copy that 'cd dir, git pull, cd ..' loop for each directory.
After that, you can setup your script to run every so often by using Windows's task scheduluer:
http://www.thewindowsclub.com/how-to-schedule-batch-file-run-automatically-windows-7Also (again, assuming windows), here's a demo on how to create a junction folder- These come in handy quite a bit.
Say you had your git repos in C:\git\ (C:\git\Ulysses for this example), and your server's addon folder is C:\SteamCMD\garrysmod\garrysmod\addons\.
In order to create a link to just ULX and ULib into your addons folder, you would open CMD as an administrator, then run the following commands:
mklink /D /J C:\SteamCMD\garrysmod\garrysmod\addons\ulx C:\git\Ulysses\ulx
mklink /D /J C:\SteamCMD\garrysmod\garrysmod\addons\ulib C:\git\Ulysses\ulib
The syntax is mklink /D /J <name of link> <target (existing) folder>.
Hope that helps!