[doc] wrote down current grammar diffing status

docs/grammar.rst

@@ -34,6 +34,18 @@ section**
 Python 3.3 is the based grammar I've started diffing with, some of the grammar
 differences marked as 3.3 are actually from older python version.
+Current status
+==============
+
+Grammar diff has been done up to python 3.6.2.
+
+Still, some stuff for the lexer are probably missing in this list like:
+
+* fstrings
+* adding _ in numbers
+
+I need to got through all release notes to see that.
+
 Print function
 ~~~~~~~~~~~~~~
@@ -336,7 +348,6 @@ After:
-
 Variables annotations
 ~~~~~~~~~~~~~~~~~~~~~
@@ -422,6 +433,7 @@ After:
+
 Nothing to do
 -------------