Include installation of SDL in documentation?

[lukehesluke]

Hi. This project is EXACTLY what I've been looking for and thank you so much for the effort in making this.

I just noticed a small thing when following the instructions to get started: If SDL2 hasn't been installed before starting, (ql:quickload :cepl.sdl2) will fail to work (this is perhaps not surprising!) stating that it cannot find libSDL2 (more detailed view of the error is included below).

For me, this was simply solved by installing SDL2 - on my OS X:

brew install sdl2

Perhaps this could be included in the C Library Dependency section of the README?

Thanks!

---

Full "cannot find libSDL2" error:

Unable to load any of the alternatives:
   ((:FRAMEWORK "SDL2") (:DEFAULT "libSDL2"))
   [Condition of type CFFI:LOAD-FOREIGN-LIBRARY-ERROR]

Restarts:
 0: [RETRY] Try loading the foreign library again.
 1: [USE-VALUE] Use another library instead.
 2: [TRY-RECOMPILING] Recompile library and try loading it again
 3: [RETRY] Retry loading FASL for #<CL-SOURCE-FILE "sdl2" "library">.
 4: [ACCEPT] Continue, treating loading FASL for #<CL-SOURCE-FILE "sdl2" "library"> as having been successful.
 5: [RETRY] Retry ASDF operation.
 --more--

Backtrace:
  0: (CFFI::FL-ERROR "Unable to load any of the alternatives:~%   ~S" ((:FRAMEWORK "SDL2") (:DEFAULT "libSDL2")))
  1: (CFFI::TRY-FOREIGN-LIBRARY-ALTERNATIVES SDL2::LIBSDL2 ((:FRAMEWORK "SDL2") (:DEFAULT "libSDL2")) NIL)
  2: ((FLET CFFI::%DO-LOAD :IN CFFI::%DO-LOAD-FOREIGN-LIBRARY) #<CFFI:FOREIGN-LIBRARY LIBSDL2> SDL2::LIBSDL2 (:OR (:FRAMEWORK "SDL2") (:DEFAULT "libSDL2")))
  3: (CFFI:LOAD-FOREIGN-LIBRARY SDL2::LIBSDL2 :SEARCH-PATH NIL)
…etc