doc: advise batching patch rerolls

doc: advise batching patch rerolls

Contributors often need guidance on how quickly to send later iterations
of a patch series. Add a rough default of no more than one new version
of the same series per day so feedback can be batched and reviewers have
time to comment regardless of their time zones.

Mention factors that can affect the timing, such as series size, review
depth, and substantial rework. Also point out that avoiding rapid
rerolls encourages authors to polish each version before sending it, so
reviewers can focus on substantial issues.

Helped-by: Patrick Steinhardt <redacted>
Signed-off-by: Weijie Yuan <redacted>
Signed-off-by: Junio C Hamano <redacted>