[Chapel Merge] Fixed minor formatting bug in primers/classes

Branch: refs/heads/master
Revision: e0df6d6
Author: lydia-duncan
Log Message:

Merge pull request #17397 from Venkatavaradan-R/primers-classes-format-fix

Fixed minor formatting bug in primers/classes
[contributed by @Venkatavaradan-R, reviewed by Lydia]

A missing breakline in primers/classes was causing a list to render incorrectly on the website.
Fixed that and modified README in doc/ directory for a bit more clarity as to when the html/ directory is generated.

The primer passed and the built docs looked good

Modified Files:
M doc/README.rst

M test/release/examples/primers/classes.chpl

Compare: https://github.com/chapel-lang/chapel/compare/446bd963730b...e0df6d6c5962