R1:59b49e642991

In Diffusion browse views, show a README file if one exists

Summary: COMPLETELY ORIGINAL IDEA

Test Plan: Browsed around Phabricator, got helpful readmes in some cases.

Reviewers: davidreuss, btrahan

Reviewed By: btrahan

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D2022