Add docker network CLI.

[philipz]

Reference the official docs, only docker network CLI.

[dimonomid]

@philipz, thanks for the contribution.

One of my goals was to have a cheat-sheet which fits into two pages, so that I can print it on both sides of a single A4 sheet, and keep it on my desktop. The proposed change adds a third page (and by the way leaves a lot of empty space, which could be utilized for something else).

I just realized it would be good to have several versions of the cheat-sheet (obviously, without duplicating the content in LaTeX sources); one way to implement it that I can think of is to have each section defined in a separate file, and have some "main" file which will include whatever section files in whatever order, to fit them best. This way, we could have multiple "main" files: at least, the one which fits into 2 pages as it is now, and the second one which includes more sections and has more pages.

Until we implement that, I'm not ready to merge it and break the 2-page layout.

[dimonomid]

Alternatively, we might have some additional, more "advanced" cheat-sheets, which can be used in addition to the "essential" one, which we have now. I'm not sure if the networking API is large enough to fill the whole 2 pages; if not, the "advanced" cheatsheet might contain all the possible options of the docker build and docker run (because this cheat-sheet contains just a small subset of these APIs), and/or something else.