Add warning about venv init steps

HPC_Python_Guide.md

@@ -56,6 +56,8 @@ To run python, remember to use the `python3` command.
 
 ## III. Virtualenv activation
 
+> __NOTE:__ These steps must be done every time. Also if you change from a login node to a GPU node (e.g. by calling `sxm2sh`)
+
 1. Navigate to your project folder.
 
 2. Load modules for Python by entering:
@@ -72,7 +74,7 @@ To run python, remember to use the `python3` command.
    source <VENV_NAME>/bin/activate
    ```
 
-To make life easy, put these commands in a bash script called `init.sh`:
+__Pro tip:__ To make life easy, put these commands in a bash script called `init.sh`:
 ```
 #!/bin/bash
 module load python3/3.8.9