doc: move README.NetConsole to HTML documentation

Convert README.NetConsole to reStructured text and move it to
doc/usage/netconsole.rst.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index af7d506..063e970 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -3,6 +3,8 @@
 
 .. toctree::
 
+   netconsole
+
 Shell commands
 --------------