SharePoint offers some markdown allowing you to easily link to wiki pages and lists / list items by use of square bracket notation. This is preferable to the "add link by address" functionality where the link is encoded in the HTML as it makes the link more transparent to the editor.
When linking to documents, it's best to link to them by ID (i.e. via the _layouts/DocIdRedir.aspx?ID=1234567 style links) as this ensures the link isn't tied to the document name (which may change).
Is there a markdown syntax for linking to documents by id?