Just add $(SRCROOT) to the Framework Search Paths in Project Build Settings (Search Paths).
Crashlytics installation process drops its Crashlytics.framework to your project folder (or creates the symlink).
If you moved Crashlytics.framework somewhere deeper in the project folder hierarchy – set ‘recursive’ to the right or just point directly to its parent folder in Header Search Paths:
$(SRCROOT)/Path/to/the/folder/containing/Crashlytics.framework