Match install instructions to tags

We're not going to be using HEAD anymore.

See varia/bibliotecha-install#4.

docs/index.md

@@ -300,18 +300,43 @@ $ dhcpcd5
 #### How to upgrade Calibre-web
 
 You'll need to re-connect your Bibliotecha to the internet with an ethernet
-cable and then run the following commands:
+cable first. Then, you'll need to check to see what are the latest releases
+from Calibre-web on [their release page]. Once you have a fair idea of the
+version you'd like to upgrade to (careful, skipping over multiple versions can
+easily break things, so better go one by one and check which one works each
+step of way), then start off with turning off the program and getting into the
+installation directory.
 
 ```bash
 $ systemctl stop cps
 $ cd /var/www/calibre-web
-$ git pull origin master
+```
+
+Now, you'll want to pull down all the tags from the remote repository.
+
+```bash
+$ git fetch origin master -a
+```
+
+Then list all those tags.
+
+```bash
+$ git tag -l
+```
+
+At this point you should see your version number listed somewhere. You can
+check check out to that tag, install the updated dependencies and restart the
+program.
+
+```bash
+$ git checkout 0.6.9  # latest version as of November 2020
 $ .venv/bin/pip install -r requirements.txt
 $ systemctl start cps
 ```
 
 [understanding bibliotecha networking]: #understanding-bibliotecha-networking
 [mailing list]: https://we.lurk.org/postorius/lists/bibliotecha.we.lurk.org/
+[their release page]: https://github.com/janeczku/calibre-web/releases/tag/0.6.9
 
 ## Manual installation