docs: add follower count section

for #1582

templates/docs.html

@@ -47,6 +47,7 @@
 <li><a href="#update-profile">How do I update my profile?</a></li>
 <li><a href="#troubleshooting">I tried it, and it didn't work!</a></li>
 <li><a href="#user-page">Can I see my account's status and recent activity?</a></li>
+<li><a href="#follower-count">How does my bridged account's follower count work?</a></li>
 <li><a href="#mention">How do I @-mention a bridged user?</a></li>
 <li><a href="#delete">How do I delete a post?</a></li>
 <li><a href="#enhanced">The <code>*.brid.gy</code> domain in my bridged account is ugly. Can I use my own domain instead?</a></li>
@@ -342,6 +343,12 @@ <h3 id="general">Using</h3>
 </p>
 </li>
 
+<li id="follower-count" class="question">How does my bridged account's follower count work?</li>
+<li class="answer">
+<p>Follower counts are inexact. Unlike profiles and posts and other interactions, we don't try too hard to match bridged accounts' follower counts with their followers across all networks. If they don't exactly reconcile, that's normal, for many possible reasons. Don't worry about it.
+</p>
+</li>
+
 
 <li id="mention" class="question">How do I @-mention a bridged user?</li>
 <li class="answer">