[clang][docs] fix rendering of $-prefixed options

This was added in llvm#117573 but the options were not being rendered
correctly due to the missing newline after `::`.

Author: carlocab

clang/docs/UsersManual.rst

@@ -1066,6 +1066,7 @@ is being invoked, and added after all of the command-line specified linker
 inputs. Here is some example of ``$``-prefixed options:
 
 ::
+
     $-Wl,-Bstatic $-lm
     $-Wl,-Bshared