docs: add link to Slack

docs/_includes/footer.html

@@ -28,15 +28,14 @@ <h3>Universe</h3>
 			<h3>Connect</h3>
 			<ul>
 				<li><a rel="me" href="https://fosstodon.org/@sitespeedio">Mastodon</a></li>
-				<li><a href="https://twitter.com/SiteSpeedio">Twitter</a></li>
-				<li><a href="https://www.facebook.com/sitespeed.io">Facebook</a></li>
 				<li><a href="https://github.com/sitespeedio">GitHub</a></li>
+				<li><a href="(https://join.slack.com/t/sitespeedio/shared_invite/zt-296jzr7qs-d6DId2KpEnMPJSQ8_R~WFw">Slack</a></li>
 		</div>
 		<div class="col-1-5">
 			<h3>sitespeed.io</h3>
 			<ul>
 				<li><a href="{{site.baseurl}}/aboutus/">About Us</a></li>
-				<li><a href="{{site.baseurl}}/important/">Important - how we work</a></li>
+				<li><a href="{{site.baseurl}}/important/">How we work</a></li>
 				<li><a href="https://dashboard.sitespeed.io/">The dashboard</a></li>
 				<li><a href="{{site.baseurl}}/logo/">Logos</a></li>
 				<li><a href="{{site.baseurl}}/privacy-policy/">Privacy Policy</a></li>
@@ -47,7 +46,6 @@ <h3>sitespeed.io</h3>
 			<h3><span class="red">&hearts;</span> Open Source <span class="red">&hearts;</span></h3>
 			<ul>
 				<li><a href="http://www.seleniumhq.org/">Selenium</a></li>
-				<li><a href="https://github.com/WPO-Foundation/visualmetrics">Visual Metrics</a></li>
 				<li><a href="https://github.com/micmro/PerfCascade">PerfCascade</a></li>
 				<li><a href="http://getskeleton.com/">Skeleton</a></li>
 				<li><a href="https://github.com/cgiffard/node-simplecrawler">Simplecrawler</a></li>