Document how to use Tails Installer to do a manual upgrade from 3.5 (#15416)

I wouldn't have used an inline if the content was meant to be used only
twice, but we should reuse it at least for the 3.6.1 release notes and
probably for 3.7 as well.

wiki/src/news/version_3.5/manual_upgrade.inline.mdwn

+   <p>If you are upgrading from Tails 3.5, it is only possible to select an
+   ISO image when running Tails in English. For other languages, the
+   file chooser button remains inactive:</p>
+
+   [[!img news/version_3.5/broken-file-chooser.png link="no"]]
+
+   <p>To do a manual upgrade from Tails 3.5, you can either:</p>
+
+   <ul>
+     <li>Restart Tails 3.5 in English</li>
+
+     <li>Start <span class="application">Tails Installer</span> in
+     English from the command line:
+
+     <pre>LANG=en_US tails-installer</pre>
+     </li>
+   </ul>

wiki/src/news/version_3.6.mdwn

@@ -100,10 +100,14 @@ See the list of [[long-standing issues|support/known_issues]].
 
 - To install, follow our [[installation instructions|install]].
 
+<a id="upgrade"></a>
+
 - We do not provide automatic upgrades from older Tails installations for
   this release, as we've hit an old bug while generating the necessary files
   ([[!tails_ticket 13426]]). You have to [[upgrade manually|upgrade]].
 
+  [[!inline pages="news/version_3.5/manual_upgrade.inline" raw="yes" sort="age"]]
+
 - [[Download Tails 3.6.|install/download]]
 
 # What's coming up?

wiki/src/upgrade/tails.mdwn

@@ -49,6 +49,14 @@ copied.</p>
 1. Choose <span class="guilabel">Use a downloaded Tails ISO
    image</span>.
 
+   <a id="3.5"></a>
+
+   <div class="bug">
+
+   [[!inline pages="news/version_3.5/manual_upgrade.inline" raw="yes" sort="age"]]
+
+   </div>
+
 1. Use the <span class="guilabel">Target Device</span> drop-down list to
    specify the intermediary USB stick.