Update install_linux.md

Nate Smith · web-flow · commit 921a2993abb7 · 2020-09-18T13:16:06.000-05:00
diff --git a/docs/install_linux.md b/docs/install_linux.md
@@ -22,9 +22,12 @@ sudo apt update
 sudo apt install gh
 ```
 
+**Note**: If you are behind a firewall, the connection to `keyserver.ubuntu.com` might fail. In that case, try running `sudo apt-key adv --keyserver keyserver.ubuntu.com:80 --recv-key C99B11DEB97541F0`.
+
 **Note**: most systems will have `apt-add-repository` already. If you get a _command not found_
 error, try running `sudo apt install software-properties-common` and trying these steps again.
 
+
 Upgrade:
 
 ```bash
