Suggest reading blead's Super Quick Patch Guide

Suggest reading blead's Super Quick Patch Guide

The Super Quick Patch Guide has been improved several times. Suggest that
a patcher looks at the latest version in the checkout of blead they've
just made, in case that's been improved since whichever released version
they were reading.

This has caught me out before: I've done something sub-optimal (for me or
those reviewing my patches) by diligently following out-of-date
instructions.

Remove trailing whitespace.

For: RT #119599