doc: describe loady command

Create a man-page for the loady command.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 317db3b..1304b59 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -20,6 +20,7 @@
    echo
    exit
    for
+   loady
    mbr
    pstore
    sbi