Fix typos like `a html` to `an html` and 'an mail' to 'an email'. [ci skip]
Merge pull request #16155 from mechanicles/fix-typos

[ci skip] Fix typos like `a html` to `an html` and 'an mail' to 'an email'.
Format pass on 4.2 release notes [ci skip]

*   Leave two blank lines between sections/packages for readibility.

*   Always indent bullet points with four spaces. This allows multi-paragraph
    points to align properly (see #16103), and it is the same as the format we
    already use in CHANGELOGs. Doing this consistently sets an easy precedent
    for future contributors to follow.

*   Always put the PR/commit link on its own line in the source. If the bullet
    point spans multiple paragraphs, put it on its own paragraph at the end.

[Godfrey Chan & Juanito Fatas]
[ci skip] Little bit doc code improvement.
Merge pull request #16156 from mechanicles/document-improvement

[ci skip] Improve documentation consistency for ActiveModel::Errors