Add a comment to the 'from-import' rule

Author: Yury Selivanov

grammars/MagicPython.syntax.yaml

@@ -568,6 +568,9 @@ repository:
               (?x) \{ [^'"}\n]*? \} (?=.*?\})
 
   from-import:
+    comment: |
+      The main purpose of this rule is to consume '...', so that
+      it's not tokenized as ellipsis.
     match: |
       (?x)
         \s* (from) (\s*\.+\s*)