Docs: Add doc. holding some setup instructions and tips for a GSE Dev VM

Add this document to provide some setup instructions and tips for making
the most of a Gnome Shell Extensions Development VM.

docs/Gnome_Shell_Extensions_Development_VM.md

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+# Gnome Shell Extensions Development VM
+
+This document holds some setup instructions and tips for getting the most of your Gnome Shell Extensions Development VM.
+
+Note on commands in this document:
+
+- `$` indicates that a command should be run as your normal user.
+- `#` indicates that a command should be run as root.
+
+## GTKInspector
+
+Enable GTKInspector by running the following command:
+
+```
+$ gsettings set org.gtk.Settings.Debug enable-inspector-keybinding true
+```
+
+Now you can inspect GTK Apps by pressing `Ctrl + Shift + D`.
+
+### Links and Sources
+
+- <https://wiki.gnome.org/Projects/GTK/Inspector>
+
+## Looking Glass
+
+Looking Glass is Gnome Shells integrated debugger and inspector tool.
+You can use it by pressing `Alt + F2`, typing `lg` and pressing Enter.
+
+If you want to exit Looking Glass, press `Esc` in the Evaluator pane.
+
+### Links and Sources
+
+- <https://wiki.gnome.org/Projects/GnomeShell/LookingGlass>
+
+## Sharing a Directory Between the Host and the Guest
+
+To share a directory between the host and the Gnome Shell Extensions Development VM, do the following.
+Note that this guide assumes you're using Virtual Machine Manager (virt-manager) and at least v4.0.0 of it.
+
+1. Shut down the VM.
+2. Go to your VMs hardware details and then to `Memory`.  
+   Check the `Enable shared memory` checkbox there.
+3. Go to your VMs hardware details and then to `Add Hardware -> Filesystem`.  
+   Then select `virtiofs` for the driver and an appropriate source path (like `/home/user/gse_dev_vm_shared_folder`) and target path (like `shared_folder`).
+   Finally click on `Finish`.
+4. Power on the VM.
+5. Create a mountpoint by running:
+
+   ```
+   # mkdir /mnt/shared_host_folder
+   ```
+
+6. Edit `/etc/fstab` and add the following line at the end:
+
+   ```
+   TARGET_PATH_YOU_SET_IN_VIRT_MANAGER /mnt/shared_host_folder virtiofs rw,noatime,_netdev 0 0
+   ```
+
+7. Reboot the VM.
+
+Now you have a shared folder between your host and your VM, which you can access on your host at the specified source path and in the VM at `/mnt/shared_host_folder`.
+
+### Links and Sources
+
+- <https://wiki.archlinux.org/title/Libvirt#Sharing_data_between_host_and_guest>
+- <https://libvirt.org/kbase/virtiofs.html>
+- <https://github.com/virt-manager/virt-manager/releases/tag/v4.0.0>
+
+## Enabling Automatic Login
+
+Enabling Automatic Login in the Gnome Settings under `Users -> Unlock... -> Automatic Login` saves you from inserting the VM users password after VM startups.
+
+## Disabling Automatic Screen Lock
+
+Disabling Automatic Screen Lock in the Gnome Settings under `Privacy -> Screen Lock -> Automatic Screen Lock` saves you from Gnome locking the VM and you having to insert the VM users password.
+
+## Running Applications Providing Tray Icons Automatically on Startup
+
+Especially for the development of this extension it is useful to have some applications, which provide tray icons (e.g. Element, Telegram) run automatically on startup.
+To make this happen (nicely), you need to do the following:
+
+1. Make sure the applications get started automatically on log in by using Gnome Tweaks, going to `Startup Applications` and adding them there.
+2. If you're using Automatic Login, use the Password and Keys application (seahorse) to set the Login keyrings password to a blank one.
+   Do this to avoid the Login keyring password prompt after log in, which is triggered by some applications like Element.
+   Note that this leaves the keyring unencrypted, but since you're in a Dev VM, no important things should be stored in there anyway (hopefully).
+3. Use the "Auto Move Windows" extension to move the windows of your applications to a different workspace, so your main one doesn't get cluttered.
+4. To see tray icons, install the "AppIndicator and KStatusNotifierItem Support" extension.
+
+### Links and Sources
+
+- <https://wiki.archlinux.org/title/GNOME/Keyring>