docs: List supported rolling upgrade paths.

The wording above is not completely clear without these scenarios
listed. A confused reader may incorrectly read it as:

```
Only LTS-to-LTS is supported for rolling upgrades.
```

which is wrong.

Signed-off-by: Ihar Hrachyshka <ihrachys@redhat.com>
Acked-by: Ales Musil <amusil@redhat.com>
Signed-off-by: Numan Siddique <numans@ovn.org>

Documentation/intro/install/ovn-upgrades.rst

@@ -74,6 +74,11 @@ To avoid buildup of complexity and technical debt we limit the span of versions
 supported for a rolling upgrade on :ref:`long-term-support` (LTS), and it
 should always be possible to upgrade from the previous LTS version to the next.
 
+The following rolling upgrade paths are supported:
+
+1. LTS to the very next LTS release, or to any non-LTS in between the two.
+2. Any non-LTS to the very next LTS release.
+
 The first LTS version of OVN was 22.03.  If you want to upgrade between other
 versions, you can use the `Fail-safe upgrade`_ procedure.