make the error message for the cli a bit more specific

src/wormhole/cli/runner.py

@@ -60,6 +60,9 @@ def run(reactor, argv, cwd, stdout, stderr, executable=None):
             print(msg, file=stderr)
             print(file=stderr)
             print(str(f.value), file=stderr)
+        elif f.check(KeyFormatError):
+            msg = textwrap.fill("ERROR: " + textwrap.dedent(f.value.__doc__))
+            print(msg, file=stderr)
         else:
             print("ERROR:", f.value, file=stderr)
         raise SystemExit(1)

src/wormhole/errors.py

@@ -39,7 +39,8 @@ class WrongPasswordError(Exception):
 class KeyFormatError(Exception):
     """
     The key you entered contains spaces. Magic-wormhole expects keys to be
-    separated by dashes.
+    separated by dashes. Please reenter the key you were given separating the
+    words with dashes.
     """
 
 class ReflectionAttack(Exception):