[SR-2960] Better Document utils/run-test

[swift-ci]

Previous ID	SR-2960
Radar	None
Original Reporter	Beingessner (JIRA User)
Type	Task

Additional Detail from JIRA

Votes	1
Component/s
Labels	Task, StarterBug
Assignee	None
Priority	Medium

md5: ba31e0f5995fad19b727242ff79320fa

Issue Description:

Neither build-script -h nor docs/Testing.rst mention the existence of utils/run-test, but they should. This is the best way to run a subset of the tests, and a huge quality-of-life improvement for working on the compiler or standard library.

[swift-ci]

Comment by Brian (JIRA)

Huge +1 here. I'd love to help out here, but I still don't think I have a good understanding of the process. I was only able to figure out a reasonable build / debug cycle from https://speakerdeck.com/ayanonagon/contributing-to-swift . Also, the trick of adding --filter=SILGen/ to lit was a huge help, but I've never used `run-test`.

[AnthonyLatsis]

Now documented here.