Add "see also" section to tldr pages

[oxguy3]

Very often, it seems like it'd be very likely that someone viewing page A might also find page B very useful. It could be very helpful if tldr pages were allowed to have a "See also" section at the bottom. For example, related or similar tools could link to each other (e.g. grep/ack, chgrp/chown, more/less, rm/shred, head/tail, etc). Another use case: sub commands and parent commands could all link to each other (e.g. git-whatever tools could link to git, and the git page could link to all of them. ditto for csvkit and all of its tools).

A very simple implementation might look like:

# foo

> Most awesome tool ever.
...

## See also
- bar: another awesome tool
- baz: legacy version of foo
- qux: for reverting the effects of foo

It shouldn't be too hard for clients to implement this (command-line clients could probably get away with printing the raw markdown, more or less, and clients that already rely on a proper Markdown library won't need to do anything).

---

Issue #784 (which I've just submitted) goes hand-in-hand with this issue. If #784 and this issue were both implemented, then the See also section would definitely make use of the link syntax, and probably look more like this:

## See also
- [bar]: another awesome tool
- [common/baz]: cross-platform version of foo
- [qux]: for reverting the effects of foo

[igorshubovych]

Just wonder, have you seen this?
tldr-pages/tldr-node-client#81

[oxguy3]

Dang, I had not seen that. Huh, well guess this is a bit redundant. >.<

[igorshubovych]

Which one is redundant? Your variant or mine?

[oxguy3]

Mine is redundant I guess, since yours was way earlier. That said, I do think it'd be nice if the see also list included descriptions of why that particular tool was being linked. And also, being able to link to specific OS versions would be nice, like I showed below the horizontal rule in my original post.

[waldyrious]

This is actually a duplicate of #481. I'll close this one and reopen the previous one :)