docs: add a top level page for bitbake documentation

The top level index file includes a link to the Bitbake
documentation. This link is static, however the location of the
Bitbake documentation depends on the intersphinx configuration. As
such, when looking at an old YP docs release, the link to the bitbake
documentation is always the same (and wrong).

Since we cannot use a cross reference in a toc index, this patch
creates an intermediate page for bitbake documentation, and in that
page we insert the right link to the bibtake documentation
(e.g. :doc:`bitbake:index`) which will be adjusted dynamically based
on intersphinx config.

(From yocto-docs rev: 4f7f451df266a307b34bf145b29291ca85eb882f)

Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Tested-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/bitbake.rst

@@ -0,0 +1,19 @@
+.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
+
+=====================
+BitBake Documentation
+=====================
+
+|
+
+BitBake was originally a part of the OpenEmbedded project. It was inspired by
+the Portage package management system used by the Gentoo Linux distribution. In
+2004, the OpenEmbedded project was split the project into two distinct pieces:
+
+-  BitBake, a generic task executor
+-  OpenEmbedded, a metadata set utilized by BitBake
+
+Today, BitBake is the primary build tool of OpenEmbedded based projects, such as
+the Yocto Project.
+
+The BitBake documentation can be found :doc:`here <bitbake:index>`.

documentation/index.rst

@@ -34,7 +34,7 @@ Welcome to the Yocto Project Documentation
    Application Development and the Extensible SDK (eSDK) <sdk-manual/index>
    Toaster Manual <toaster-manual/index>
    Test Environment Manual <test-manual/index>
-   Bitbake User Manual <https://docs.yoctoproject.org/bitbake>
+   bitbake
 
 .. toctree::
    :maxdepth: 1