docs: fix link, reformat credits file

Author: zsquareplusc

CONTRIBUTING.rst

@@ -43,4 +43,4 @@ Ownership
 
 .. _CREDITS.rst: CREDITS.rst
 .. _issue: https://github.com/pyserial/pyserial-asyncio/issues
-.. _wellcome: https://github.com/pyserial/pyserial-asyncio/pulls
+.. _welcome: https://github.com/pyserial/pyserial-asyncio/pulls

CREDITS.rst

@@ -2,16 +2,20 @@
  Credits
 =========
 
-Main authors of pySerial-asyncio:
+Main authors of pySerial-asyncio
+================================
 
 - Chris Liechti (zsquareplusc)
 - Robert Smallshire (rob-smallshire)
 
 
-Contributions by:
+Contributors
+============
 
 - David Ko
 - Nicolas Di Pietro
 - jabdoa2
-- ... not all names may be listed here, see also ``git log``
+- ... not all names may be listed here, see also ``git log`` or online history_
 
+
+.. _history: https://github.com/pyserial/pyserial-asyncio/commits/master