doc: shorten overlong title underlines

Title underlines should match the length of the title. Unfortunately
docutils only catches underlines that are too short.

Add some missing empty lines after titles.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/usage/cmd/coninfo.rst b/doc/usage/cmd/coninfo.rst
index f913148..76cb6c3 100644
--- a/doc/usage/cmd/coninfo.rst
+++ b/doc/usage/cmd/coninfo.rst
@@ -21,7 +21,7 @@
 list of device names.
 
 Example
---------
+-------
 
 .. code-block:: console