add 2 missing man page files to cabal file

Only useful when using cabal install to install it with man pages.
It's hard to remember to list new man page files here.

git-annex.cabal

@@ -48,6 +48,7 @@ Extra-Source-Files:
   doc/git-annex-assistant.mdwn
   doc/git-annex-calckey.mdwn
   doc/git-annex-checkpresentkey.mdwn
+  doc/git-annex-config.mdwn
   doc/git-annex-contentlocation.mdwn
   doc/git-annex-copy.mdwn
   doc/git-annex-dead.mdwn
@@ -128,6 +129,7 @@ Extra-Source-Files:
   doc/git-annex-uninit.mdwn
   doc/git-annex-unlock.mdwn
   doc/git-annex-untrust.mdwn
+  doc/git-annex-unregisterurl.mdwn
   doc/git-annex-unused.mdwn
   doc/git-annex-upgrade.mdwn
   doc/git-annex-vadd.mdwn