Update getting started instructions for airstack (#327)

* Update getting started instructions for airstack

Add command to source .bashrc for airstack usage

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Co-authored-by: Andrew Jong <ajong@andrew.cmu.edu>

Author: DevRobi

docs/getting_started/index.md

@@ -33,6 +33,7 @@ cd AirStack
 ```bash
 ./airstack.sh install  # installs docker, docker-compose, and the NVIDIA Container Toolkit
 ./airstack.sh setup  # this lets you use the `airstack` command and sets up your keys
+source ~/.bashrc  # execute and apply settings in ~/.bashrc to enable airstack command
 ```
 
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