add Brotli support! via requests 2.26 and Google's brotli library

fixes #878

requirements.txt

@@ -8,6 +8,7 @@ git+https://github.com/snarfed/oauth-dropins.git#egg=oauth_dropins
 git+https://github.com/snarfed/granary.git#egg=granary
 git+https://github.com/kylewm/mf2util.git#egg=mf2util
 git+https://github.com/Alir3z4/html2text.git#egg=html2text
+brotli~=1.0
 cachetools~=4.2
 gdata-python3~=3.0
 google-cloud-error-reporting~=1.2

templates/about.html

@@ -555,8 +555,6 @@ <h3 id="listen">Pulling back responses</h3>
 </p>
 
 <p>Twitter, Instagram, Flickr, and GitHub only allow one web site link in your profile, so Bridgy <a href="https://github.com/snarfed/bridgy/issues/483">also looks for links in your profile's description field</a>. Reddit doesn't have a spot for any website links so Bridgy just searches your profile description.</p>
-
-<p>Also, if your web server has <a href="https://brotli.org/">Brotli compression</a> enabled, Bridgy won't work with it due to <a href="https://issuetracker.google.com/issues/112277350">this long-standing App Engine bug</a>. <a href="https://github.com/snarfed/bridgy/issues/878">More background.</a> Until this bug is fixed, we recommend disabling Brotli on your web server as a workaround.</p>
 </li>
 
 <li id="order" class="question">Why are the Bridgy comments on my site out of