R1:cae8c49745cc

Fix diffusion.readmequery to work in a cluster enviroment

Summary:
Ref T2783. This method is kind of goofballs:

- We send a big list of paths to it.
- It sends back a giant blob of HTML.

Instead, just figure out the path we want locally, then fetch the content with `diffusion.filecontentquery`.

Test Plan:
- Viewed main view and directory view, saw a README.
- See screenshots.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T2783

Differential Revision: https…