Update copyright attribution line (#705)

https://smallbusiness.chron.com/year-copyright-statement-mean-62027.html
https://squidfunk.github.io/mkdocs-material/setup/setting-up-the-footer/#custom-copyright
https://github.com/squidfunk/mkdocs-material/releases/tag/8.0.0

mkdocs.yml

@@ -2,7 +2,7 @@ site_name: 'Pi-hole documentation'
 site_url: 'https://docs.pi-hole.net/'
 repo_url: 'https://github.com/pi-hole/pi-hole'
 edit_uri: '../docs/blob/master/docs/'
-copyright: 'Copyright © 2022 Pi-hole LLC'
+copyright: 
 remote_branch: gh-pages
 theme:
   name: 'material'

overrides/main.html

@@ -1,8 +0,0 @@
-{% extends "base.html" %}
-
-{% set extracopyright %}
-  <br>
-  <a href="https://www.netlify.com/" target="_blank" rel="noopener noreferrer">
-    This site is powered by Netlify
-  </a>
-{% endset %}

overrides/partials/copyright.html

@@ -0,0 +1,7 @@
+<div style="display:block">
+Copyright Pi-hole. Licensed under <a href="http://creativecommons.org/licenses/by-sa/4.0/" target="_blank" rel="noopener noreferrer">CC BY-SA 4.0</a>
+<br>
+<a href="https://www.netlify.com/" target="_blank" rel="noopener noreferrer">
+  This site is powered by Netlify
+</a>
+</div>