[containers] Updated docs, added comments per PR comments v3

Author: eshvk

docs/Using-Docker.md

@@ -31,10 +31,7 @@ Unity environment **has** to be built for the **linux platform**. When building
 
 Then click `Build`, pick an environment name (e.g. `3DBall`) and set the output directory to `unity-volume`. After building, ensure that the file `<environment-name>.x86_64` and subdirectory `<environment-name>_Data/` are created under `unity-volume`.
 
-![Build Settings For Docker(Without Headless)](images/docker_build_settings_noheadless.png)
-
-![Build Settings For Docker (Headless Mode)](images/docker_build_settings_headless.png)
-
+![Build Settings For Docker](images/docker_build_settings.png)
 
 ### Build the Docker Container