Added credentials

scribblings/git.scrbl

@@ -15,6 +15,8 @@ The short form is intended for build scripts and interactive use:
 (require git)
 
 (git 'status)
+(git 'diff)
+(git 'diff '--cached)
 (git 'add "main.rkt" "info.rkt")
 (git 'commit "Implement raco support")
 (git 'tag "v0.1")
@@ -54,6 +56,10 @@ Calls @racket[git], displays its result in a compact human-readable form, and re
 
 @defproc[(git-clean?) boolean?]{Returns @racket[#t] when @racket[git-status] is empty.}
 
+@defproc*([[(git-diff) string?]
+           [(git-diff [option (or/c '--cached)]) string?]])]{Returns a unified patch as a string. With no arguments it compares the index with the worktree, like @tt{git diff}. With @racket['--cached] it compares HEAD with the index, like @tt{git diff --cached}.}
+
+
 @defproc[(git-add [path path-string?] ...) void?]{Stages the given paths. With no paths, stages the whole repository, including tracked removals.}
 
 @section{Configuration and commits}