Instead of use 'docs/*.md' in dep5. For clarity and avoiding a wide-
matching wildcard.
+ Remove mention of old files from .reuse/dep5
+ add info to .github/dependabot.yml
+ make scripts/copyright.pl warn on non-matching patterns
Closes#13245
Assisted-by: Daniel Gustafsson
Assisted-by: Rich Salz
Assisted-by: Hugo van Kemenade
Assisted-by: James Fuller
Assisted-by: Marc Hörsken
Assisted-by: Jay Satiro
Closes#5555