refactor: Reformat link table template in README

[tpoliaw]

Having the source and repo link as a 'normal' row makes it clearer what
is going on and stops 'Source' looking like a description of the other
link types.

[coretl]

Happy with the What/Where change, but not with the whitespace changes.
Requirements for the expanded template:

• If docker==False or similar, there should be no empty line in the table
• For each row in the table, the cell widths should be the same as the previous row

The only way I could find to make this happen was the contorted {% ... %} syntax that was in there before

[tpoliaw]

Turns out when you use a local clone of a template, copier still uses a tagged version not the checked out version. Have reverted the contortions but left the if true blocks replaced with comments.