The pull-requests.md document has gotten quite out of date. This commit
does a massive scrub of its content for completeness, accuracy and
readability. A number of links are fixed, updated information on labels
and bot commands is added, workflow descriptions for test and merge are
updated, and a description of the KEP process is added.
Understanding the pull request process is central to being a successful
contributor. This commit moves it from the more technical k8s internals
detailed devel/ area over to the guide/ where it will get more
visibility.
This patch just moves the file and leaves a tombstone reminder
behind.
Tim Pepper