Add info for events backlog and scope

[BretFisher]

Fixes #727

- What I did

1. Add docker events description info on the two scope types of events.
2. Add docker events note in two places about backlog limit of event log.

- How I did it
After testing and using the events feature and discovering these undocumented things, I edited some markdown lines with my bare hands :)

- How to verify it
Like @joaofnfernandes mentioned in docker/docs#5432 (comment) we may need @cpuguy83 and/or @thaJeztah to validate the 1000 message buffer limit.

- Description for the changelog

Added documentation on docker events scope and buffer limits.

- A picture of a cute animal (not mandatory but encouraged)

Signed-off-by: Bret Fisher bret@bretfisher.com

[codecov-io]

Codecov Report

Merging #809 into master will decrease coverage by 2.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #809      +/-   ##
==========================================
- Coverage   52.95%   50.91%   -2.04%     
==========================================
  Files         244      237       -7     
  Lines       15839    15332     -507     
==========================================
- Hits         8387     7807     -580     
- Misses       6898     7025     +127     
+ Partials      554      500      -54

[vdemeester]

LGTM 🐸

[thaJeztah]

Thanks! Left a suggestion, but let me know what you think 👍

[thaJeztah]

If this is a "note", this should use our standard markup for notes:

> **Note**: There is a limited backlog of events you can filter. `docker events`
> is  a rolling log, and has at most 1000 events at a time.

However, trying to preserve "notes" for exceptional cases; perhaps this can be rephrased slightly to not be a "note". Something like:

Docker uses a rolling log to store the last 1000 events, which means that at
most 1000 events at a time are returned.

(not entirely happy with that example; perhaps you have a better suggestion)

[mdlinville]

How about just "Only the last 1000 log events are returned. You can use filters to further limit the number of events returned."

[mdlinville]

How about just "Only the last 1000 log events are returned. You can use filters to further limit the number of events returned."

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "patch-1" git@github.com:BretFisher/cli.git somewhere
$ cd somewhere
$ git rebase -i HEAD~842354655680
editor opens
change each 'pick' to 'edit'
save the file and quit
$ git commit --amend -s --no-edit
$ git rebase --continue # and repeat the amend for each commit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[BretFisher]

ping @thaJeztah and @MistyHacks

[thaJeztah]

changes LGTM, but erm.. could you squash your commits?

[mdlinville]

I updated the title to not include an issue number in it, since the title will become the commit message, and would ping issue 727 every time it hits a different branch or even gets put into a different repo (like docker/docker-ce). This kind of info is best left in the description like you already have it.

[thaJeztah]

Ah, yes, bet to remove that from the commit description (GitHub is a pain in that respect) 😅

[thaJeztah]

carried / squashed in #1999