Use explicit links for documentation cross-references

[trey-stafford]

Our documentation has a fair number of cross-references that link to other parts of the documentation. In these cases, we have generally used the /path/to/md_file.md#specific-reference-by-header-title style of referencing. E.g.,

[How to contribute styles](/contributor/how-to/contribute-styles.md)

Explicit references provide more flexibility and are not tied to specific files/header sections. This would allow us to refactor docs more easily.