Change single link and add frozenlist. (#6875)

* Change single link and add frozenlist

* Update README.rst

* Typo and fix to cononical url

README.rst

@@ -166,13 +166,15 @@ Requirements
 - charset-normalizer_
 - multidict_
 - yarl_
+- frozenlist_
 
 Optionally you may install the cChardet_ and aiodns_ libraries (highly
 recommended for sake of speed).
 
 .. _charset-normalizer: https://pypi.org/project/charset-normalizer
 .. _aiodns: https://pypi.python.org/pypi/aiodns
 .. _multidict: https://pypi.python.org/pypi/multidict
+.. _frozenlist: https://pypi.org/project/frozenlist/
 .. _yarl: https://pypi.python.org/pypi/yarl
 .. _async-timeout: https://pypi.python.org/pypi/async_timeout
 .. _cChardet: https://pypi.python.org/pypi/cchardet