RFR: 7903683 Document how to run individual self-tests [v2]

[Ludvig Janiuk]

> Add documentation on how to run individual self-tests with their ".ok" files to building.md.

Ludvig Janiuk has updated the pull request incrementally with three additional commits since the last revision:

 - typo
 - typos
 - update with pointer to test/README

-------------

Changes:
  - all: https://git.openjdk.org/jtreg/pull/184/files
  - new: https://git.openjdk.org/jtreg/pull/184/files/be2dce7f..8d10fcae

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=184&range=01
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=184&range=00-01

  Stats: 8 lines in 2 files changed: 4 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jtreg/pull/184.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/184/head:pull/184

PR: https://git.openjdk.org/jtreg/pull/184