Add a link to binman's documentation and adjust the files so that it is
accessible. Use the name README.rst so it is easy to discover when binman
is installed without U-Boot.

Signed-off-by: Simon Glass <sjg@chromium.org>

These docs are useful for developers, not users. Move them under that
section.

Suggested-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>

Much of the content here is useful only for development. Move it under
that section.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

Add a second on writing tests, covering when to use Python and C, where
to put the tests, etc. Add a link to the existing Python test
documentation.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add details about how to run a sandbox test directly, without using
pytest. This is more convenient for rapid development, since it is faster
and allows easier use of a debugger. Also mention sandbox_flattree as an
example of the different sandbox builds available.

Signed-off-by: Simon Glass <sjg@chromium.org>

There are quite a few available version options in U-Boot. Add a list of
the available Makefile variables and #defines, along with examples.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

Convert README.menu to reStructured text and add it to the HTML
documentation.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

Convert test/py/README.md to restructured text and add it to the generated
HTML documentation.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

Move test/README to the 'Develop U-Boot' chapter of the HTML documentation.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

Provide sub-chapters for 'Develop U-Boot'

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>