haskell-users-guide.md: document static linking

doc/haskell-users-guide.md

···
    The same thing applies to `cabal configure`, of course, if you're
    building with `cabal-install` instead of Stack.
 
+## Creating statically linked binaries
+
+There are two levels of static linking. The first option is to configure the
+build with the Cabal flag `--disable-executable-dynamic`. In Nix expressions,
+this can be achieved by setting the attribute:
+
+    enableSharedExecutables = false;
+
+That gives you a binary with statically linked Haskell libraries and
+dynamically linked system libraries.
+
+To link both Haskell libraries and system libraries statically, the additional
+flags `--ghc-option=-optl=-static --ghc-option=-optl=-pthread` need to be used.
+In Nix, this is accomplished with:
+
+    configureFlags = [ "--ghc-option=-optl=-static" "--ghc-option=-optl=-pthread" ];
+
+It's important to realize, however, that most system libraries in Nix are built
+as shared libraries only, i.e. there is just no static library available that
+Cabal could link!
+
 
 # Other resources