Fix broken links

Author: samoht

README.md

@@ -47,7 +47,7 @@ $ opam install git
   position-independent representation so that they can be manipulated
   more easily. Pack file can be created but will not be compressed yet.
 
-* The [index file] (http://mirage.github.io/ocaml-git/Index.html)
+* The [index file] (https://github.com/samoht/ocaml-git/blob/master/lib/index.mli)
   (used as for managing the stagging area)
   are fully supported. Which means that `git diff` and `git status`
   will work as expected on a repository created by the library.
@@ -63,7 +63,7 @@ $ opam install git
 * An abstraction for Git [Store](http://mirage.github.io/ocaml-git/Store.S.html)
   is available. Various store implementations are available:
   - An [in-memory](http://mirage.github.io/ocaml-git/Memory.html) implementation;
-  - A [unix filesystem](http://mirage.github.io/ocaml-git/Git_unix.FS.html)
+  - A [unix filesystem](http://mirage.github.io/ocaml-git/Git_unix.S.FS.html)
     implementation;
   - A [mirageOS](http://mirage.github.io/ocaml-git/Git_mirage.html) implementation,
     requiring an `V1_LWT.FS` implementation.