Add the describe command

...which should, hopefully, show useful information about a particular
YANG node, such as the YANG-level description, the units, type info,
etc.

Change-Id: Id430ae58fe353124e5132fa5a69378e98932ebce
diff --git a/tests/example-schema.yang b/tests/example-schema.yang
index cbd5d8d..f876779 100644
--- a/tests/example-schema.yang
+++ b/tests/example-schema.yang
@@ -57,6 +57,7 @@
     }
 
     leaf leafDecimal {
+        units "nm";
         type decimal64 {
             fraction-digits 9;
         }