* Avoid two step navigation to get to the description of the write command.
* Add missing index entries
* Correct formatting of the examples.
* Describe configuration and return value.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

Add the description of CLI commands to the generated index.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

The read and write commands are, deliberately, implemented in the same
file, so that they stay feature-compatible (e.g. if someone implements
support for "read the full partition, however large that is", that
same syntax should also work for write). In order to ensure the
documentation for both are similarly kept in sync, and to avoid
duplication, document them both in read.rst, and add a stub write.rst
referring to read.rst.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Simon Glass <sjg@chromium.org>