I have downloaded the library:
git clone https://github.com/groue/GRMustache
I got this error:
GRMustache/Classes/GRMustacheNSUndefinedKeyExceptionGuard.m:24:9: fatal error: 'JRSwizzle.h' file not found 
1 error generated.
The problem is that the file belongs to other project jrswizzle that somehow althought is linked in github is not downloaded
The issue is solved just downloading the project:
git clone https://github.com/groue/jrswizzle.git
If there is a better way to download the project from git it would be great if it is documented.
Anyway, thank you for the library!
Document git submodules for issue #12
Yes, there is a better solution.
GRMustache has git submodules, as the .gitmodules file tells you. You should thus delete your manually-crafted Libs/groue/jrswizzle folder, and run this command instead:
git submodule update --init
This will download all repositories GRMustache depends on, and allow you to build the library.
BTW, just to make things clear: GRMustache ships with already-built libraries : you don't need to run the make command, unless you have changed GRMustache's code. In order to use GRMustache, read guides/embedding.md. If you plan to change it, read guides/forking.md.