Update SETUP.md

Fix SETUP screenshot links
Merge pull request #1 from scottostler/patch-1

Update SETUP.md
Use readonly submodules for mynetwork/myutilities
Add iOS 5 support to knobs
Disable plugins depending on NSMapTable on iOS5
Update SETUP.md

Add 'git submodule update' to Setup instructions
Merge pull request #2 from scottostler/patch-2

Update SETUP.md
Minor changes to setup instructions
Update SETUP.md to include adding -ObjC and CFNetworking/Security frameworks

I also took a screenshot of the linker settings here if you want to add it to the repo: http://cl.ly/image/0e230v3Z0O2f
Merge pull request #3 from scottostler/patch-4

Update SETUP.md to include -ObjC flag and CFNetworking/Security frameworks
Add objc-linker screenshot