Documentation: correct and expand the markdown instructions for a link (#2106)

* correcting and expanding the markdown instructions for a link
- "some content" in `[some content](https://somelink/)` is called the
    content of an entity (or alt text for an image link)
- "some title" in this example is the the title element of the
    entity: `[some content](https://somelink/ "some title")`

* link description: Fixed a typo, restructured a line break I screwed up, and I cleaned up the language a bit