doc: toolchain: ATfE: fix formating

This commit fixe text formatting, removing numbered paragraphs, and
adding sub-titled parts.

Signed-off-by: Alex Fabre <alex.fabre@rtone.fr>

Author: AlexFabre

doc/develop/toolchains/arm_toolchain_for_embedded.rst

@@ -3,84 +3,85 @@
 Arm Toolchain for Embedded (ATfE)
 #################################
 
-#. LLVM toolchain by ARM
 
-   #. Arm Toolchain for Embedded (ATfE) is a C and C++ toolchain from Arm based
-      on the free and open-source LLVM Compiler Infrastructure and the Picolib C
-      library for baremetal targets.
+Arm Toolchain for Embedded (ATfE) is a C and C++ toolchain from Arm based
+   on the free and open-source LLVM Compiler Infrastructure and the Picolib C
+   library for baremetal targets.
 
-   #. ATfE is fined-tuned with a particular focus on performance for newer
-      ARM products (post 2024) like 64-bit Arm Architectures (AArch64),
-      or the M-Profile Vector Extension (MVE, a 32-bit Armv8.1-M extension).
+ATfE is fined-tuned with a particular focus on performance for newer
+   ARM products (post 2024) like 64-bit Arm Architectures (AArch64),
+   or the M-Profile Vector Extension (MVE, a 32-bit Armv8.1-M extension).
 
-#. Installation
+Installation
+************
 
-   #. Download and install a `Arm toolchain for embedded`_ build for your operating system
-      and extract it on your file system.
+#. Download and install a `Arm toolchain for embedded`_ build for your operating system
+   and extract it on your file system.
 
-   #. :ref:`Set these environment variables <env_vars>`:
+#. :ref:`Set these environment variables <env_vars>`:
 
-      - Set :envvar:`ZEPHYR_TOOLCHAIN_VARIANT` to ``llvm``.
-      - Set :envvar:`LLVM_TOOLCHAIN_PATH` to the toolchain installation directory.
+   - Set :envvar:`ZEPHYR_TOOLCHAIN_VARIANT` to ``llvm``.
+   - Set :envvar:`LLVM_TOOLCHAIN_PATH` to the toolchain installation directory.
 
-   #. To check that you have set these variables correctly in your current
-      environment, follow these example shell sessions (the
-      :envvar:`LLVM_TOOLCHAIN_PATH` values may be different on your system):
+#. To check that you have set these variables correctly in your current
+   environment, follow these example shell sessions (the
+   :envvar:`LLVM_TOOLCHAIN_PATH` values may be different on your system):
 
-      .. tabs::
+   .. tabs::
 
-         .. group-tab:: Ubuntu
+      .. group-tab:: Ubuntu
 
-            .. code-block:: bash
+         .. code-block:: bash
 
-               echo $ZEPHYR_TOOLCHAIN_VARIANT
-               llvm
-               echo $LLVM_TOOLCHAIN_PATH
-               /home/you/Downloads/ATfE
+            echo $ZEPHYR_TOOLCHAIN_VARIANT
+            llvm
+            echo $LLVM_TOOLCHAIN_PATH
+            /home/you/Downloads/ATfE
 
-         .. group-tab:: macOS
+      .. group-tab:: macOS
 
-            .. code-block:: bash
+         .. code-block:: bash
 
-               echo $ZEPHYR_TOOLCHAIN_VARIANT
-               llvm
-               echo $LLVM_TOOLCHAIN_PATH
-               /home/you/Downloads/ATfE
+            echo $ZEPHYR_TOOLCHAIN_VARIANT
+            llvm
+            echo $LLVM_TOOLCHAIN_PATH
+            /home/you/Downloads/ATfE
 
-         .. group-tab:: Windows
+      .. group-tab:: Windows
 
-            .. code-block:: powershell
+         .. code-block:: powershell
 
-               > echo %ZEPHYR_TOOLCHAIN_VARIANT%
-               llvm
-               > echo %LLVM_TOOLCHAIN_PATH%
-               C:\ATfE
+            > echo %ZEPHYR_TOOLCHAIN_VARIANT%
+            llvm
+            > echo %LLVM_TOOLCHAIN_PATH%
+            C:\ATfE
 
-      .. _toolchain_env_var:
+   .. _toolchain_env_var:
 
-   #. You can also set ``ZEPHYR_TOOLCHAIN_VARIANT`` and ``LLVM_TOOLCHAIN_PATH`` as CMake
-      variables when generating a build system for a Zephyr application, like so:
+#. You can also set ``ZEPHYR_TOOLCHAIN_VARIANT`` and ``LLVM_TOOLCHAIN_PATH`` as CMake
+   variables when generating a build system for a Zephyr application, like so:
 
-         .. code-block:: console
+      .. code-block:: console
 
-         west build ... -- -DZEPHYR_TOOLCHAIN_VARIANT=llvm -DLLVM_TOOLCHAIN_PATH=...
+      west build ... -- -DZEPHYR_TOOLCHAIN_VARIANT=llvm -DLLVM_TOOLCHAIN_PATH=...
 
-#. Toolchain settings
+Toolchain settings
+******************
 
-   #. Because LLVM is widely compatible with GNU tools, When builiding with any
-      LLVM toolchain, you have to specify some settings to let the compiler
-      know what tools to use:
+Because LLVM is widely compatible with GNU tools, When builiding with any
+   LLVM toolchain, you have to specify some settings to let the compiler
+   know what tools to use:
 
-   #. Linker:
-      Set :envvar:`CONFIG_LLVM_USE_LLD=y` to use LLVM linker.
-      set :envvar:`CONFIG_LLVM_USE_LD=y` to use the GNU LD linker.
+Linker:
+   Set :envvar:`CONFIG_LLVM_USE_LLD=y` to use LLVM linker.
+   set :envvar:`CONFIG_LLVM_USE_LD=y` to use the GNU LD linker.
 
-   #. Runtime library:
-      Set :envvar:`CONFIG_COMPILER_RT_RTLIB=y` to use LLVM runtime library.
-      Set :envvar:`CONFIG_LIBGCC_RTLIB=y` to use LibGCC runtime library.
+Runtime library:
+   Set :envvar:`CONFIG_COMPILER_RT_RTLIB=y` to use LLVM runtime library.
+   Set :envvar:`CONFIG_LIBGCC_RTLIB=y` to use LibGCC runtime library.
 
-   .. code-block:: console
+.. code-block:: console
 
-      west build ... -- -DZEPHYR_TOOLCHAIN_VARIANT=llvm -DLLVM_TOOLCHAIN_PATH=... -DCONFIG_LLVM_USE_LLD=y -DCONFIG_COMPILER_RT_RTLIB=y
+   west build ... -- -DZEPHYR_TOOLCHAIN_VARIANT=llvm -DLLVM_TOOLCHAIN_PATH=... -DCONFIG_LLVM_USE_LLD=y -DCONFIG_COMPILER_RT_RTLIB=y
 
 .. _Arm Toolchain for Embedded: https://developer.arm.com/Tools%20and%20Software/Arm%20Toolchain%20for%20Embedded