Merge branch 'doc/add-info-about-overidding-app-host' into 'master'

Add docs about overriding host with host file

This MR adds a note to `set-up-gdk.md` about using `./host` file to override host the workhorse process will bind to.

This is especially useful when someone uses GDK inside the Docker container and wants to expose Workhorse.

See merge request !180

doc/set-up-gdk.md

@@ -94,6 +94,10 @@ You can override the port used by this GDK with a 'port' file.
     echo 4000 > port
+Similarly, you can override the host (for example if you plan to use GDK inside a Docker container).
+
+    echo 0.0.0.0 > host
+
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