Add documentation about how to compile the client on Windows with Qt6.

Signed-off-by: Camila Ayres <hello@camilasan.com>

doc/dev/compiling-on-windows-qt6.rst

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+Compiling the desktop client on Windows with Qt6
+================================================
+
+System requirements
+-------------------
+- Windows 10 or Windows 11
+- `The desktop client code <https://github.com/nextcloud/desktop>`_  
+- Python 3
+- PowerShell
+- Microsoft Visual Studio 2022 and tools to compile C++
+- `KDE Craft <https://community.kde.org/Craft>`_
+
+
+Setting up Microsoft Visual Studio
+----------------------------------
+
+- Click on 'Modify' in the Visual Studio Installer:
+
+  .. image:: ./images/dev/visual-studio-installer.png
+    :alt: Visual Studio Installer
+
+- Select 'Desktop development with C++'
+
+  .. image:: ./images/dev/desktop-development-with-cpp.png
+    :alt: Desktop development with C++
+
+Handling the dependencies 
+-------------------------
+
+We decided to use `KDE Craft <https://community.kde.org/Craft>`_ to get all binary dependencies of the desktop client.
+because it is convenient to mantain and to set it up.
+
+- Set up KDE Craft as instructed in `Get Involved/development/Windows - KDE Community Wiki <https://community.kde.org/Get_Involved/development/Windows>`_ -  it requires Python 3 and PowerShell.
+- After running:
+
+.. code-block:: winbatch
+
+   C:\CraftRoot\craft\craftenv.ps1
+
+- Add the desktop client blueprints - the instructions to handle the client dependencies:
+
+.. code-block:: winbatch
+
+  craft --add-blueprint-repository [git]https://github.com/nextcloud/desktop-client-blueprints.git
+  craft craft
+
+- Install all client dependencies:
+
+.. code-block:: winbatch
+
+  craft --install-deps nextcloud-client
+
+Compiling
+---------
+
+- Make sure your environment variable %PATH% has the possible minimum 
+- Open the Command Prompt (cmd.exe)
+- Run:
+
+.. code-block:: winbatch
+
+  "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvarsall.bat" x64
+
+- To use the tools installed with Visual Studio, you need the following in your %PATH%:
+
+  .. image:: ./images/dev/path.png
+    :alt: Windows environment variables    
+
+- Alternatively you can use the tools installed with KDE Craft by adding them to %PATH%:
+
+.. code-block:: winbatch
+
+  set "PATH=C:\CraftRoot\bin;C:\CraftRoot\dev-utils\bin;%PATH%"
+
+.. note::
+  C:\CraftRoot is the path used by default by KDE Craft. When you are setting it up you may choose a different folder.
+
+- Create build folder, run cmake, compile and install:
+
+.. code-block:: winbatch
+
+  cd <desktop-repo-path>
+  mkdir build
+  cd build
+  cmake .. -G Ninja -DCMAKE_INSTALL_PREFIX=. -DCMAKE_PREFIX_PATH=C:\CraftRoot -DCMAKE_BUILD_TYPE=RelWithDebInfo
+  cmake --build . --target install
+  
+After this, you can use `Qt Creator <https://doc.qt.io/qtcreator>`_ to import the build folder with its configurations to be able to work with the code.
+
+