docs: update readme style
docs: update readme style

Using MarkdownLint in VSCode, this file was showing many linter errors,
mostly around whitespace issues, but a few others that made it annoying
enough when looking at the file, it was inconsistent and difficult to
read.

Also handles a few existing notes about caching.

Refs #412
Resolves #420
Resolves #424

Signed-off-by: Mike Fiedler <af44b651315133051dded0e55830cbf76e9bfef9@gmail.com>

UnitedIncome/serverless-python-requirements,UnitedIncome/serverless-python-requirements