Update docs on internal linking

[Cwpute]

Did a bit of internal linking for my blog, and had a difficult time understanding how it worked.
You have currently two articles talking about it: Anatomy of a post and Navigation. The former has partial information about how it all works, compared to the second, which still lacks some critical information i had to research myself.

The informations that were lacking were about subheaders and internal link formatting, which were both consisely explained here:

First, i'd suggest that the section in Anatomy of a post talking about links should provide a shortcut to Navigation for explaination in more details, and second, that you include the above missing informations i had struggle with in Navigation.

Thanks !

[andrei-akopian]

As a sidenote in case anybody wants to spread more knowledge:

The #link-to-section actually refer to HTML element ids like the #id syntax in CSS.

If a paragraph has an id you can link to it.

<p id="test"><a href="#test">Test Link<a><p>

Test Link

The internal linking is more HTML than Markdown. Linking to headings requires markdown converter to specifically generate the ids.