Added Ubuntu 20.04 to install-manual.md

Author: craigloewen-msft

WSL/install-manual.md

@@ -18,6 +18,8 @@ In these cases, while WSL itself is available, how do you download and install L
 ## Downloading distros
 
 If the Microsoft Store app is not available, you can download and manually install Linux distros by clicking these links:
+* [Ubuntu 20.04](https://aka.ms/wslubuntu2004)
+* [Ubuntu 20.04 ARM](https://aka.ms/wslubuntu2004arm)
 * [Ubuntu 18.04](https://aka.ms/wsl-ubuntu-1804)
 * [Ubuntu 18.04 ARM](https://aka.ms/wsl-ubuntu-1804-arm)
 * [Ubuntu 16.04](https://aka.ms/wsl-ubuntu-1604)