doc: qfw man-page

Provide a man-page for the qfw command.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 7dca913..a8842bf 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -28,5 +28,6 @@
    loady
    mbr
    pstore
+   qfw
    sbi
    true