Updated Compile firmware (markdown)

Compile-firmware.md

@@ -39,6 +39,8 @@ Finally, create a `build` folder inside of the repository. From Github Desktop,
 
 ## Step 3: Prepare the Docker container
 _Note: You need to make sure you have also cloned the hackrf folder. to do that run: ```git submodule update --init --recursive```_
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 Open up a terminal in the root of the cloned git repo and run: ```docker run -t portapack-dev -f dockerfile-nogit . ```
 
 After its built the docker image, go back to docker and you should see this screen under images