Fix instructions on how to rebuild some modules

Lib/keyword.py

@@ -7,7 +7,7 @@ This file is automatically generated; please don't muck it up!
 To update the symbols in this file, 'cd' to the top directory of
 the python source tree after building the interpreter and run:
 
-    python Lib/keyword.py
+    ./python Lib/keyword.py
 """
 
 __all__ = ["iskeyword", "kwlist"]

Lib/symbol.py

@@ -7,7 +7,7 @@
 #  To update the symbols in this file, 'cd' to the top directory of
 #  the python source tree after building the interpreter and run:
 #
-#    python Lib/symbol.py
+#    ./python Lib/symbol.py
 
 #--start constants--
 single_input = 256

Lib/token.py

@@ -7,7 +7,7 @@ __all__ = ['tok_name', 'ISTERMINAL', 'ISNONTERMINAL', 'ISEOF']
 #  To update the symbols in this file, 'cd' to the top directory of
 #  the python source tree after building the interpreter and run:
 #
-#    python Lib/token.py
+#    ./python Lib/token.py
 
 #--start constants--
 ENDMARKER = 0