Add an example in the README

Author: samoht

README.md

@@ -79,6 +79,37 @@ $ opam install git
 
 Performance is comparable to the Git tool.
 
+### Example
+
+```ocaml
+# require "git.unix";;
+# open Lwt.Infix;;
+# open Git_unix;;
+# module Search = Git.Search(FS);;
+
+# let read file =
+    FS.create () >>= fun t ->
+    FS.read_reference_exn t Git.Reference.master >>= fun head ->
+    Search.find t (Git.SHA.of_commit head) (`Commit (`Path file)) >>= function
+    | None     -> failwith "file not found"
+    | Some sha -> FS.read_exn t sha >>= function
+      | Git.Value.Blob b -> Lwt.return (Git.Blob.to_raw b)
+      | _ -> failwith "not a valid path"
+ ;;
+ val read : string list -> string Lwt.t = <fun>
+
+# Lwt_main.run (read ["README.md"] >|= print_string)
+
+Pure OCaml low-level bindings to Git -- Guaranteed no C inside.
+
+Support for on-disk and in-memory Git stores. Can read and write all
+the Git objects: the usual blobs, trees, commits and tags but also
+the pack files, pack indexes and the index file (where the staging area
+lives).
+
+[...]
+```
+
 ### License
 
 MIT, see LICENSE file for its text.