doc: gs: Clearly state the main dependencies min version

Introduce a table with the minimum version required for the three main
dependencies (CMake, Python and DTC). At the same time remove the CMake
help code from the GSG, since it's just a duplicate of the instructions
that Kitware provides.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
Co-authored-by: Ruth Fuchss <ruth.fuchss@nordicsemi.no>

doc/getting_started/index.rst

@@ -53,6 +53,23 @@ Install dependencies
 
 Next, you'll install some host dependencies using your package manager.
 
+The current minimum required version for the main dependencies are:
+
+.. list-table::
+   :header-rows: 1
+
+   * - Tool
+     - Min. Version
+
+   * - `CMake <https://cmake.org/>`_
+     - 3.13.1
+
+   * - `Python <https://www.python.org/>`_
+     - 3.6
+
+   * - `Devicetree compiler <https://www.devicetree.org/>`_
+     - 1.4.6
+
 .. tabs::
 
    .. group-tab:: Ubuntu
@@ -68,33 +85,15 @@ Next, you'll install some host dependencies using your package manager.
               python3-dev python3-pip python3-setuptools python3-tk python3-wheel xz-utils file \
               make gcc gcc-multilib g++-multilib libsdl2-dev
 
-      #. Verify the version of cmake that is installed on your system by entering::
+      #. Verify the versions of the main dependencies installed on your system by entering::
 
             cmake --version
+            python3 --version
+            dtc --version
 
-         The version must be 3.13.1 or later. If your version is older, complete the following
+         Check those against the versions in the table in the beginning of this section.
-         steps to add the `Kitware third-party apt repository <https://apt.kitware.com/>`__,
+         Refer to the :ref:`installation_linux` page for additional information on updating
-         which contains an updated version of cmake.
+         the dependencies manually.
-
-         a) Add the Kitware signing key:
-
-            .. code-block:: bash
-
-               wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | sudo apt-key add -
-
-         b) Add the Kitware apt repository for your OS release. For Ubuntu
-            18.04 LTS:
-
-            .. code-block:: bash
-
-               sudo apt-add-repository 'deb https://apt.kitware.com/ubuntu/ bionic main'
-
-         c) Then install the updated version of cmake with ``apt``:
-
-            .. code-block:: bash
-
-               sudo apt update
-               sudo apt install cmake
 
    .. group-tab:: macOS
 

doc/getting_started/installation_linux.rst

@@ -125,9 +125,9 @@ need one.
 CMake
 =====
 
-CMake version 3.13.1 or higher is required. Check what version you have by
+A :ref:`recent CMake version <install-required-tools>` is required. Check what
-using ``cmake --version``. If you have an older version, there are several ways
+version you have by using ``cmake --version``. If you have an older version,
-of obtaining a more recent one:
+there are several ways of obtaining a more recent one:
 
 * On Ubuntu, you can follow the instructions for adding the
   `kitware third-party apt repository <https://apt.kitware.com/>`_
@@ -187,16 +187,16 @@ versions.)
 DTC (Device Tree Compiler)
 ==========================
 
-A recent DTC version (1.4.6 or higher) is required. Check what version you
+A :ref:`recent DTC version <install-required-tools>` is required. Check what
-have by using ``dtc --version``. If you have an older version, either install a
+version you have by using ``dtc --version``. If you have an older version,
-more recent one by building from source, or use the one that is bundled in
+either install a more recent one by building from source, or use the one that is
-the :ref:`Zephyr SDK <zephyr_sdk>` by installing it.
+bundled in the :ref:`Zephyr SDK <zephyr_sdk>` by installing it.
 
 Python
 ======
 
-Python 3.6 or later is required. Check what version you have by using ``python3
+A `modern Python 3 version <install-required-tools>` is required. Check what
---version``.
+version you have by using ``python3 --version``.
 
 If you have an older version, you will need to install a more recent Python 3.
 You can build from source, or use a backport from your distribution's package