CFC: normative terms in non-normative section on microsyntax

Issue #622 notes that section 5.6 of the Activity Vocabulary document
includes RFC 2119 terms like MAY, SHOULD, and SHOULD NOT, even though the
section is non-normative:

https://github.com/w3c/activitystreams/issues/622

I've added a PR for an erratum to note this error:

https://github.com/w3c/activitystreams/pull/627

The erratum reads:

The second paragraph in the non-normative section "Mentions, Tags and Other
Common Social Microsyntaxes" contains RFC 2119 capitalized terms like MAY,
SHOULD NOT, and SHOULD, which gives the impression that the requirements
are normative. One solution is to replace the capitalized terms with
equivalent terms that don't suggest normative requirements: 'While such
microsyntaxes can be used within the values of the `content`, `name`, and
`summary` properties on an Activity Streams Object, implementations are not
required to parse the values of those properties in order to determine the
appropriate routing of notifications, categorization, or linking between
objects. Instead, publishers make appropriate use of the vocabulary terms
provided specifically for these purposes.'


This is a call for consensus. If there are no objections in the next 14
calendar days, I will apply this PR to the errata file, and update the
editor's draft to include the new wording.

Thanks,

Evan