updated a broken link to Python Magic Methods#774

Merged

kennethreitz merged 3 commits intorealpython:masterfrom

hector12free:master

Nov 30, 2016

Commits on Nov 30, 2016

Fixed broken link on Magic Methods with new link and a brief note. The original website is down.
hector12free
committed
Change the link to Magic Methods from its GitHub repo to its pdf file directly.
hector12free
committed
Format note according to the Style Guide
hector12free
committed