Improve bug report template on GitHub (#5259)

Only show in developer changelog

.github/ISSUE_TEMPLATE/--bug-report.yml

@@ -1,12 +1,17 @@
 name: "🐛Bug report"
 description: "Create a bug report about GDevelop or the game engine"
 body:
+  - type: checkboxes
+    attributes:
+      label: Is there an existing issue for this?
+      options:
+      - label: I have searched the [existing issues](https://github.com/4ian/GDevelop/issues)
+        required: true
   - type: textarea
     attributes:
       label: Describe the bug
       description: |
         A clear and concise description of what the bug is.
-        Please double check that the bug is not already reported in the issues list.
     validations:
       required: true
   - type: textarea
@@ -36,18 +41,20 @@ body:
   - type: input
     attributes:
       label: GDevelop version
-      description: Which version of GDevelop are you using?
+      description: |
+        Which version of GDevelop are you using?
+        Take a look here: [Editor Home - About GDevelop - "This version of GDevelop is: ~~~"]
       placeholder: 5.1.159? 5.1.160?
     validations:
       required: true
   - type: textarea
     attributes:
       label: Platform info
       value: |
-        OS: 
-        OS Version: 
-        Browser(For Web): 
-        Device(For Mobile): 
+        OS: (e.g. Windows, Linux, macOS, Android, iOS)
+        OS Version: (e.g. Windows 10, macOS 10.15)
+        Browser(For Web): (e.g. Chrome, Firefox, Safari)
+        Device(For Mobile): (e.g. iPhone 12, Samsung Galaxy S21)
   - type: textarea
     attributes:
       label: Additional context