dev-manual/bmaptool.rst: simplify and fix instructions

- Remove duplicate instructions

- Detail how to run bmaptool directly if you installed it on your host
  instead of building it through the ``bmaptool-native`` recipe,
  as running "oe-run-native bmaptool-native bmaptool ..." won't work
  in this case.

- Use "chmod a+w" instead of "chmod 666", better advice,
  and only run "chmod" in the option that runs "oe-run-native"

(From yocto-docs rev: 4afa71ef6e5bf1db126c80e6d987f588d0b5a086)

Signed-off-by: Michael Opdenacker <michael.opdenacker@rootcommit.com>
Reviewed-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/dev-manual/bmaptool.rst

@@ -43,14 +43,13 @@ any type of image. Use these steps to flash an image using `bmaptool`:
    depending on your particular setup. The following commands assume the
    image resides in the :term:`Build Directory`'s ``deploy/images/`` area:
 
-   -  If you have write access to the media, use this command form::
+   -  If you installed the package for `bmaptool`, you can directly run::
 
-         $ oe-run-native bmaptool-native bmaptool copy build-directory/tmp/deploy/images/machine/image.wic /dev/sdX
+         $ sudo bmaptool copy build-directory/tmp/deploy/images/machine/image.wic /dev/sdX
 
-   -  If you do not have write access to the media, set your permissions
-      first and then use the same command form::
+   -  Otherwise, if you built `bmaptool` with BitBake, run::
 
-         $ sudo chmod 666 /dev/sdX
+         $ sudo chmod a+w /dev/sdX       # get write access to the media, needed only once after booting
          $ oe-run-native bmaptool-native bmaptool copy build-directory/tmp/deploy/images/machine/image.wic /dev/sdX
 
 For help on the ``bmaptool`` command, use the following command::