[3.5] bpo-28929: Add to Misc/NEWS (GH-285)

mention bpo-28929 in the Documentation section of
What's New in Python 3.5.4 release candidate 1

Author: Mariatta

Misc/NEWS

@@ -92,6 +92,8 @@ C API
 Documentation
 -------------
 
+- bpo-28929: Link the documentation to its source file on GitHub.
+
 - bpo-25008: Document smtpd.py as effectively deprecated and add a pointer to
   aiosmtpd, a third-party asyncio-based replacement.