Create Developer-Guide_Building-with-Multipass.md (#392)

Description of Building with Docker

docs/Developer-Guide_Building-with-Multipass.md

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+# Building with Multipass
+
+In order to build an Armbian image from scratch, whether for development purposes or to [apply user customizations](https://docs.armbian.com/Developer-Guide_User-Configurations/) on top of a base image, a build environment is required. Per the Armbian documentation, Ubuntu 22.04 is [the officially supported](https://docs.armbian.com/Developer-Guide_Build-Preparation/) build platform. 
+
+[Multipass](https://multipass.run/) that is designed for quick and painless provisioning of Ubuntu VMs.
+
+
+### Creating a VM and preparing for build
+
+Multipass is [available](https://multipass.run/install) for macOS, Windows and Linux platforms.
+
+Once you have multipass installed, a Jammy (22.04) instance with 4 CPUs, 4GB of RAM and 25GB of space available can be provisioned with a single command:
+
+```bash
+multipass launch --cpus 4 --disk 25G --mem 4G --name jammy
+```
+
+### Clone the build repo
+
+You can run commands direct on the instance to clone the build repo:
+
+```bash
+multipass exec jammy -- bash -c "git clone --depth 1 https://github.com/armbian/build" 
+```
+
+### Use an instance
+Then you can get a shell to the instance and run the build as needed:
+
+```bash
+C:\> multipass shell armbian
+Welcome to Ubuntu 22.04.1 LTS (GNU/Linux 5.4.0-48-generic x86_64)
+Last login: Tue Jan 30 12:23:08 2024 from 172.22.111.1
+# Let's get building!  
+ubuntu@armbian:~$ cd build
+ubuntu@armbian:~/build$ ./compile.sh BOARD=orangepizero ... etc
+```
+
+### Share data with an instance
+
+The recommended way to share data between your host and an instance with Multipass is the command:mount
+```bash
+multipass mount /my/dir jammy
+multipass info jammy
+```
+
+Mounts:         /my/dir => /my/dir
+
+From this point on will be available inside the instance./my/dir