[doc] document f-string inclusion

CHANGELOG

@@ -12,6 +12,7 @@ Changelog
 Python 3 parsing:
 - support ellipsis https://github.com/PyCQA/baron/pull/121 by odcinek
 - support matrix operator https://github.com/PyCQA/baron/pull/117 by odcinek
+- support f-strings https://github.com/PyCQA/baron/pull/110 by odcinek
 0.6.6 (2017-06-12)
 ------------------

docs/grammar.rst

@@ -92,6 +92,18 @@ Baron: https://github.com/PyCQA/baron/pull/117
     term: factor (('*'|'@'|'/'|'%'|'//') factor)*
+
+f-strings
+---------
+
+Python 3.6
+
+Baron: https://github.com/PyCQA/baron/pull/110
+
+::
+
+    add f'' rf'' fr'' to the lexer
+
 TODO
 ====