This was not documented and its usage is going to increase massively
once users start using bitbake-setup. Add a description for this file as
well as an example on how bitbake-setup shares it for multiple builds,
to insist on the "site-wide" usage of this file.
(From yocto-docs rev: 42f68f7de7f0cf74ebdd31fae3173dd3a80386ff)
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>