Update bug report to include app version (oppia#3819)

* Update bug report to include app version

Add app version to bug report & refine a few other aspects of the template.

* Update bug_report.md

Indicate how the environment questions should be filled in.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -20,12 +20,13 @@ Steps to reproduce the behavior:
 **Expected behavior**
 A clear and concise description of what you expected to happen.
 
-**Screenshots**
+**Demonstration**
 If applicable, add screenshots or videos to help explain your problem.
 
-**Device**
-- Device/emulator being used
-- SDK version
+**Environment**
+- Device/emulator being used: <device version/emulator>
+- Android or SDK version (e.g. Android 5 or SDK 21): <os/sdk version>
+- App version (you can get this through system app settings or via the admin controls menu in-app): <app version>
 
 **Additional context**
 Add any other context about the problem here.