Add proxy server question to issue template

.github/ISSUE_TEMPLATE.md

@@ -4,4 +4,8 @@ Output of the `ue4-docker info` command:
 FULL OUTPUT OF ue4-docker info GOES HERE
 ```
 
-(The rest of the issue description goes here. If you're reporting a problem with building the container images, be sure to include the full output of the `ue4-docker build` command, along with the command line parameters used to invoke the build. If you're making a feature request, you can remove the template contents entirely, since the `ue4-docker info` output is only needed for helping diagnose and reproduce bugs.)
+Additional details:
+
+- Are you accessing the network through a proxy server? **Yes/No**
+
+(The rest of the issue description goes here. If you're reporting a problem with building container images, be sure to include the full output of the `ue4-docker build` command, including the initial output lines that display the command line parameters used to invoke the build. If you're making a feature request, you can remove the template contents entirely, since the `ue4-docker info` output and related information is only needed for helping diagnose and reproduce bugs.)