hls-graph.cabal: link to actual readme (#2404)

* hls-graph.cabal: link to actual readme

* Add readme to package

Co-authored-by: Javier Neira <atreyu.bbb@gmail.com>

hls-graph/hls-graph.cabal

@@ -3,7 +3,7 @@ name:          hls-graph
 version:       1.5.1.1
 synopsis:      Haskell Language Server internal graph API
 description:
-  Please see the README on GitHub at <https://github.com/haskell/haskell-language-server#readme>
+  Please see the README on GitHub at <https://github.com/haskell/haskell-language-server/tree/master/hls-graph#readme>
 
 homepage:      https://github.com/haskell/haskell-language-server#readme
 bug-reports:   https://github.com/haskell/haskell-language-server/issues
@@ -18,6 +18,9 @@ data-files:
     html/profile.html
     html/shake.js
 
+extra-source-files:
+    README.md
+
 flag pedantic
   description: Enable -Werror
   default:     False