add some missing doc images in a valid path

we cannot use doc/images/building folder name due to some gitignore
rules

so let's rename it to doc/images/dev

Signed-off-by: Matthieu Gallien <matthieu.gallien@nextcloud.com>

doc/building.rst

@@ -220,12 +220,12 @@ Setting up Microsoft Visual Studio
 
 1. Click on 'Modify' in the Visual Studio Installer:
 
-  .. image:: ./images/building/visual-studio-installer.png
+  .. image:: ./images/dev/visual-studio-installer.png
     :alt: Visual Studio Installer
 
 2. Select 'Desktop development with C++'
 
-  .. image:: ./images/building/desktop-development-with-cpp.png
+  .. image:: ./images/dev/desktop-development-with-cpp.png
     :alt: Desktop development with C++
 
 Handling the dependencies 
@@ -265,7 +265,7 @@ Compiling
 
 4. To use the tools installed with Visual Studio, you need the following in your %PATH%:
 
-  .. image:: ./images/building/path.png
+  .. image:: ./images/dev/path.png
     :alt: Windows environment variables    
 
 5. Alternatively you can use the tools installed with KDE Craft by adding them to %PATH%: