Adding docker install info for Ubuntu.

linux/Docker-Setup.md

@@ -0,0 +1,28 @@
+# Docker Setup on Linux (Ubuntu)
+Docker Docs Install Instructions: https://docs.docker.com/engine/install/ubuntu/#prerequisites
+- Works for Ubuntu before 20.04
+- If on 20.04 use below instructions in conjunction with the docs *until a 20.04 version is released*.
+
+## Ubuntu 20.04
+Specifically the add-apt-repository command in the docs does not work because 20.04 focal release is not available.
+Follow these instructions: https://askubuntu.com/questions/1230189/how-to-install-docker-community-on-ubuntu-20-04-lts
+Instead of:
+```
+$ sudo add-apt-repository \
+   "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
+   $(lsb_release -cs) \
+   stable"
+```
+
+use
+
+```
+$ sudo add-apt-repository \
+   "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
+   bionic \
+   stable"
+```
+
+### Removing incorrect apt-repository
+Use `sudo add-apt-repository -r` to remove:
+`sudo add-apt-repository -r "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"`

linux/Environment-Setup.md

@@ -4,6 +4,8 @@
 
 - Git: `sudo apt install git`
 - Curl: `sudo apt install curl`
+- Docker: [Ubuntu Install](https://docs.docker.com/engine/install/ubuntu/#prerequisites)
+  - [Install instructions](../master/linux/Docker-Setup.md)
 
 ### [Linux Brew](https://docs.brew.sh/Homebrew-on-Linux)