Fix bug, add docs

lark/tree.py

@@ -171,9 +171,15 @@ def find_data(self, data: str) -> 'Iterator[Tree[_Leaf_T]]':
 
 ###}
 
-    def find_token(self, typ: str) -> Iterator[_Leaf_T]:
-        """Returns all tokens whose type equals the given typ."""
-        return self.scan_values(lambda v: isinstance(v, Token) and v.type == typ)
+    def find_token(self, token_type: str) -> Iterator[_Leaf_T]:
+        """Returns all tokens whose type equals the given token_type.
+
+        This is a recursive function that will find tokens in all the subtrees.
+
+        Example:
+            >>> term_tokens = tree.find_token('TERM')
+        """
+        return self.scan_values(lambda v: not isinstance(v, Tree) and v.type == token_type)
 
     def expand_kids_by_data(self, *data_values):
         """Expand (inline) children with any of the given data values. Returns True if anything changed"""