ghc-compact: Update cabal file

Improve documentation, bump bounds and cabal-version.

libraries/ghc-compact/ghc-compact.cabal

+cabal-version:  1.12
 name:           ghc-compact
 version:        0.1.0.0
 -- NOTE: Don't forget to update ./changelog.md
@@ -19,8 +20,10 @@ description:
     Internally, the struct is stored a single contiguous block of memory,
     which allows efficient serialization and deserialization of structs
     for distributed computing.
+
+    This package provides a low-level API; see also the </package/compact
+    compact package> which provides a user-facing API.
 build-type:     Simple
-cabal-version:  >=1.10
 tested-with:    GHC==7.11
 
 source-repository head
@@ -38,7 +41,7 @@ library
 
   build-depends: ghc-prim   >= 0.5.3 && < 0.9,
                  base       >= 4.9.0 && < 4.17,
-                 bytestring >= 0.10.6.0
+                 bytestring >= 0.10.6.0 && <0.12
   ghc-options: -Wall
 
   exposed-modules: GHC.Compact