doc: fix typo and tighten wording in error sections

Changes:
- Removed superfluous "when possible"
- Fixed typo in "documentationt"
- Added missing comma
- Moved definition of error union type up to first sentence
3e836f5516Jay Weisskopf committed on 3/25/2018, 10:48:07 PM· committed by GitHubparentaa2995e
1 file changedLine totals unavailable