docs: nsqd durable restart/reload semantics

[james-lawrence]

is there a safe way to restart a nsq process? didn't see any mention of this in the documentation.

[ploxiln]

If you send nsqd SIGINT or SIGTERM it will save messages which are in each channel's memory-queue to disk, as well as in-flight and deferred messages. When it starts up again these messages will be loaded back into the appropriate topic memory-queue.

You're right, I can't easily find anywhere this is stated in the documentation.

[mreiferson]

going to update this issue to reflect the need for doc updates, thanks.

[mreiferson]

moving this issue to https://github.com/nsqio/nsqio.github.io