Add an indent option for preamble text.
Review Request #11697 — Created July 1, 2021 and submitted
Preamble text is free-form text that's often user-provided. As such,
it's important to avoid parsing issues due to that text.
Git solves this by indenting this content 4 spaces. We're leaving
indentation as a recommendation, and adding an
preamble sections to hint to the parser how much space to strip away
from each line.
Built the docs. Checked the code samples and new text for errors.