Create manual testing documentation procedure (#14776)
Commonly tested components of NVDA should have standard test plans.
This gives contributors a base manual testing plan when creating PRs that touch these NVDA components.
This also gives alpha/beta testers a base test plan for NVDA.
Description of user facing changes
None
Description of development approach
A directory has been created, ./tests/manual, which contains markdown files group by the NVDA component, e.g. "addon store", "start up / shutdown", "speech dictionaries", "settings", etc.
The goal is to document manual test plans for commonly tested NVDA components.
