doc: Expand FAQ on email usage

See https://www.reddit.com/r/qutebrowser/comments/o7stdc/comment/ipritx9/?context=3

doc/faq.asciidoc

@@ -158,7 +158,7 @@ It also works nicely with rapid hints:
 :bind ;M hint --rapid links spawn umpv {hint-url}
 ----
 
-How do I use qutebrowser with mutt?::
+How do I use qutebrowser with mutt/neomutt or other mail clients?::
     For security reasons, local files without `.html` extensions aren't
     rendered as HTML, see
     https://bugs.chromium.org/p/chromium/issues/detail?id=777737[this Chromium issue]
@@ -166,8 +166,29 @@ How do I use qutebrowser with mutt?::
     extension:
 +
 ----
-    text/html; qutebrowser %s; needsterminal; nametemplate=%s.html
+text/html; qutebrowser %s; needsterminal; nametemplate=%s.html
 ----
++
+Note that you might want to add additional options to qutebrowser, so that it
+runs as a seperate instance configured to disable JavaScript and avoid network
+requests, in order to avoid privacy leaks when reading mails. The easiest way
+to do so is by specifying a non-existent proxy server, e.g.:
++
+----
+qutebrowser --temp-basedir -s content.proxy http://localhost:666 -s content.javascript.enabled false %s
+----
++
+With Qt 6, using something like:
++
+----
+qutebrowser --temp-basedir -s content.dns_prefetch false -s content.javascript.enabled false %s
+----
++
+should lead to a similar result, due to a more restrictive implementation of
+the `content.local_content_can_access_remote_urls` setting (`false` by default
+already). However, it's advised to use a page like
+https://www.emailprivacytester.com/[Email Privacy Tester] to verify your
+configuration.
 
 What is the difference between bookmarks and quickmarks?::
     Bookmarks will always use the title of the website as their name, but with quickmarks