sphinx: import docs

The Yocto Project docs was migrated from Docbook to Sphinx in YP
 3.2. This 3.1 is an LTS release, and since 3.1 docs are 'close to'
 the docs in 3.2, we agreed to backport sphinx docs onto 3.1.

This first patch brings all changes done in 3.2 until:
7f64574f7 README: include detailed information about sphinx

There are other changes after this commit, but they will be
 selectively backported in individual patches.

This patch was generated with the following command:

git cherry-pick -n \
 $(git log --reverse --oneline \
 ac352ad7f95db7eeacb53c2778caa31800bd7c26..7f64574f7 \
| cut -f1 -d' ')

The following commits were applies in the dunfell docs, but not in
master, so they were first reverted (and squashed into this change). A
commit will reintroduce the content from these patches in the Sphinx
files in a followup patch.

069c27574 Documenation: Prepared for the 3.1.1 release
bd140f0f9 Documentation: Add 3.1.1 version updates missing from previous commit
17cc71a8f Documenation: Prepared for the 3.1.2 release
1a69e2c02 Documenation: Prepared for the 3.1.3 release
8910ac1c7 Documenation: Prepared for the 3.1.4 release

(From yocto-docs rev: c25fe058b88b893b0d146f3ed27320b47cdec236)

Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 166 insertions, 0 deletions

diff --git a/documentation/ref-manual/ref-varlocality.rst b/documentation/ref-manual/ref-varlocality.rst
new file mode 100644
index 0000000000..a95504b571
--- /dev/null
+++ b/documentation/ref-manual/ref-varlocality.rst
@@ -0,0 +1,166 @@
+.. SPDX-License-Identifier: CC-BY-2.0-UK
+
+****************
+Variable Context
+****************
+
+While you can use most variables in almost any context such as
+``.conf``, ``.bbclass``, ``.inc``, and ``.bb`` files, some variables are
+often associated with a particular locality or context. This chapter
+describes some common associations.
+
+.. _ref-varlocality-configuration:
+
+Configuration
+=============
+
+The following subsections provide lists of variables whose context is
+configuration: distribution, machine, and local.
+
+.. _ref-varlocality-config-distro:
+
+Distribution (Distro)
+---------------------
+
+This section lists variables whose configuration context is the
+distribution, or distro.
+
+-  :term:`DISTRO`
+
+-  :term:`DISTRO_NAME`
+
+-  :term:`DISTRO_VERSION`
+
+-  :term:`MAINTAINER`
+
+-  :term:`PACKAGE_CLASSES`
+
+-  :term:`TARGET_OS`
+
+-  :term:`TARGET_FPU`
+
+-  :term:`TCMODE`
+
+-  :term:`TCLIBC`
+
+.. _ref-varlocality-config-machine:
+
+Machine
+-------
+
+This section lists variables whose configuration context is the machine.
+
+-  :term:`TARGET_ARCH`
+
+-  :term:`SERIAL_CONSOLES`
+
+-  :term:`PACKAGE_EXTRA_ARCHS`
+
+-  :term:`IMAGE_FSTYPES`
+
+-  :term:`MACHINE_FEATURES`
+
+-  :term:`MACHINE_EXTRA_RDEPENDS`
+
+-  :term:`MACHINE_EXTRA_RRECOMMENDS`
+
+-  :term:`MACHINE_ESSENTIAL_EXTRA_RDEPENDS`
+
+-  :term:`MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS`
+
+.. _ref-varlocality-config-local:
+
+Local
+-----
+
+This section lists variables whose configuration context is the local
+configuration through the ``local.conf`` file.
+
+-  :term:`DISTRO`
+
+-  :term:`MACHINE`
+
+-  :term:`DL_DIR`
+
+-  :term:`BBFILES`
+
+-  :term:`EXTRA_IMAGE_FEATURES`
+
+-  :term:`PACKAGE_CLASSES`
+
+-  :term:`BB_NUMBER_THREADS`
+
+-  :term:`BBINCLUDELOGS`
+
+-  :term:`ENABLE_BINARY_LOCALE_GENERATION`
+
+.. _ref-varlocality-recipes:
+
+Recipes
+=======
+
+The following subsections provide lists of variables whose context is
+recipes: required, dependencies, path, and extra build information.
+
+.. _ref-varlocality-recipe-required:
+
+Required
+--------
+
+This section lists variables that are required for recipes.
+
+-  :term:`LICENSE`
+
+-  :term:`LIC_FILES_CHKSUM`
+
+-  :term:`SRC_URI` - used in recipes that fetch local or remote files.
+
+.. _ref-varlocality-recipe-dependencies:
+
+Dependencies
+------------
+
+This section lists variables that define recipe dependencies.
+
+-  :term:`DEPENDS`
+
+-  :term:`RDEPENDS`
+
+-  :term:`RRECOMMENDS`
+
+-  :term:`RCONFLICTS`
+
+-  :term:`RREPLACES`
+
+.. _ref-varlocality-recipe-paths:
+
+Paths
+-----
+
+This section lists variables that define recipe paths.
+
+-  :term:`WORKDIR`
+
+-  :term:`S`
+
+-  :term:`FILES`
+
+.. _ref-varlocality-recipe-build:
+
+Extra Build Information
+-----------------------
+
+This section lists variables that define extra build information for
+recipes.
+
+-  :term:`DEFAULT_PREFERENCE`
+
+-  :term:`EXTRA_OECMAKE`
+
+-  :term:`EXTRA_OECONF`
+
+-  :term:`EXTRA_OEMAKE`
+
+-  :term:`PACKAGECONFIG_CONFARGS`
+
+-  :term:`PACKAGES`