Merge ~ines-almeida/launchpad:update-lxc-distro-in-starter-docs into launchpad:master

[Ines Almeida]

Update lp's container distro from 16.04 to 18.04 in starter docs

We ask users to create a 16.04 container in the started docs, which more often than not leads to issues (e.g. the IPv4 of the container not being available). This is not an issue with ubuntu 18.04 as far as I've seen it, so it will make the setup process easier and more error proof.

I have been running launchpad locally with 18.04, and all tests pass. So far 2 other people that I know of are also using 18.04 with success.

[Simone Pelosi (pelpsi)]

LGTM!

review: Approve

[Colin Watson (cjwatson)]

Let's use 20.04, please.

diff --git a/doc/how-to/running.rst b/doc/how-to/running.rst
index a217a19..d471c19 100644
--- a/doc/how-to/running.rst
+++ b/doc/how-to/running.rst
@@ -15,6 +15,8 @@ isolate it from the rest of your system.
 After you've done this, you may want to read about
 :doc:`../explanation/navigating`.
 
+.. _supported_operating_systems:
+
 Supported operating systems
 ===========================
 
@@ -118,13 +120,20 @@ installed and configured on your network.
         path: $HOME
     EOF
 
-2. Create a container.  This command creates a Ubuntu 16.04 unprivileged
+2. Create a container. This command creates a Ubuntu 20.04 unprivileged
    container using the profile created in the previous step.
 
 .. code-block:: sh
 
-    lxc launch ubuntu:16.04 lpdev -p default -p $USER
+    lxc launch ubuntu:20.04 lpdev -p default -p $USER
+
+.. note::
+    Note that as of now, Launchpad still runs on `ubuntu:16.04` in production, 
+    but will be upgraded to `20.04` in the near future.
 
+    You can use `ubuntu:16.04` in the command above instead, but note that for
+    more recent Ubuntu versions (22.04 and above) it might need some extra steps 
+    (see note in :ref: `Supported Operating Systems <supported_operating_systems>`).
 
 .. note::
    If the command above fails with ``Error: No root device could be found``, you may need to run