Add dkms guide for armhf

recipes/dkms.md

@@ -20,14 +20,23 @@ sudo apt-get install dkms git-core
 
 ## Install DKMS (armhf)
 
-**This currently does not work due to missing `gcc-aarch64-linux-gnu`.**
+
+You have to perform additional steps to prepare `aarch64` compilation environment:
+
+```bash
+sudo apt-get update -y
+sudo apt-get install -y debootstrap dkms git-core
+sudo debootstrap --arch=arm64 --variant=minbase --include=gcc bionic /opt/gcc-arm64 http://ports.ubuntu.com/ubuntu-ports/
+echo "export CROSS_COMPILE=/opt/gcc-arm64/usr/bin/aarch64-linux-gnu-" | sudo tee /etc/dkms/framework.conf
+```
 
 ## Wireguard
 
 Installing Wireguard is very simple with DKMS and makes Wireguard to be auto-updated
 after kernel change.
 
-Following the documentation from https://www.wireguard.com/install/:
+Following the documentation from https://www.wireguard.com/install/ Ubuntu,
+visit the wireguard webpage for Debian documentation:
 
 ```bash
 sudo add-apt-repository ppa:wireguard/wireguard