update testplan with docker instructions for mac / linux (microsoft#12940)

Co-authored-by: Ian Huff <ianhuff@ravikun-dev2.redmond.corp.microsoft.com>

Author: IanMatthewHuff

.github/test_plan.md

@@ -576,23 +576,29 @@ def test_failure():
  1. Run a cell on the host
  1. Verify the editor opens on the guest and the cell is run there too
 - [ ] Jupyter Hub support
- 1. Install Docker Desktop onto a machine
- 1. Create a folder with a file 'Dockerfile' in it.
- 1. Mark the file to look like so:
-
- ``` 
- ARG BASE_CONTAINER=jupyterhub/jupyterhub
- FROM $BASE_CONTAINER
-
- USER root
-
- USER $NB_UID
- ```
-
- 1. From a command prompt (in the same folder as the Dockerfile), run ```docker build -t jupyterhubcontainer:1.0 .```
- 1. Run ```docker container create --name jupyterhub jupyterhubcontainer:1.0 jupyterhub```
- 1. From the docker desktop app, start the jupyterhub container. 
- 1. From the docker desktop app, run the CLI 
+ 1. Windows install instructions
+ 1. Install Docker Desktop onto a machine
+ 1. Create a folder with a file 'Dockerfile' in it.
+ 1. Mark the file to look like so:
+
+ ``` 
+ ARG BASE_CONTAINER=jupyterhub/jupyterhub
+ FROM $BASE_CONTAINER
+
+ USER root
+
+ USER $NB_UID
+ ```
+
+ 1. From a command prompt (in the same folder as the Dockerfile), run ```docker build -t jupyterhubcontainer:1.0 .```
+ 1. Run ```docker container create --name jupyterhub jupyterhubcontainer:1.0 jupyterhub```
+ 1. From the docker desktop app, start the jupyterhub container. 
+ 1. From the docker desktop app, run the CLI 
+ 1. OR Mac / Linux install instructions
+ 1. Install docker
+ 1. From the terminal ```docker run -p 8000:8000 -d --name jupyterhub jupyterhub/jupyterhub jupyterhub```
+ 1. Open a terminal in the docker container with ```docker exec -it jupyterhub bash```
+ 1. From that terminal run ```python3 -m pip install notebook```
  1. From the new command prompt, run ```adduser testuser```
  1. Follow the series of prompts to add a password for this user
  1. Open VS code