Improve docs for html-location

Someone mentioned this section was confusing in #haskell. I added an
example of command line usage so there is no confusion.

[ci skip]

Cabal/doc/nix-local-build.rst

@@ -1829,6 +1829,7 @@ running ``setup haddock``. (TODO: Where does the documentation get put.)
     ``haddock`` command).
 
 .. cfg-field:: haddock-html-location: templated path
+               --html-location=TEMPLATE
     :synopsis: Haddock HTML templates location.
 
     Specify a template for the location of HTML documentation for
@@ -1839,15 +1840,19 @@ running ``setup haddock``. (TODO: Where does the documentation get put.)
 
     ::
 
-        html-location: 'http://hackage.haskell.org/packages/archive/$pkg/latest/doc/html'
+        html-location: http://hackage.haskell.org/packages/archive/$pkg/latest/doc/html
+
+    The command line variant of this flag is ``--html-location`` (for
+    the ``haddock`` subcommand).
+
+    ::
+
+        --html-location='http://hackage.haskell.org/packages/archive/$pkg/latest/doc/html'
 
     Here the argument is quoted to prevent substitution by the shell. If
     this option is omitted, the location for each package is obtained
     using the package tool (e.g. ``ghc-pkg``).
 
-    The command line variant of this flag is ``--html-location`` (for
-    the ``haddock`` subcommand).
-
 .. cfg-field:: haddock-executables: boolean
     :synopsis: Generate documentation for executables.