doc: coninfo man-page

Provide a man-page for the coninfo command.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 729541b..cdf7109 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -39,6 +39,7 @@
    cmd/cbsysinfo
    cmd/cls
    cmd/cmp
+   cmd/coninfo
    cmd/conitrace
    cmd/cyclic
    cmd/dm