Update issue templates

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Use Github issues ONLY for validated bugs. PLEASE DISCUSS THEM ON THE FORUM FIRST!**
+
+We have a really active forum to help answering questions (https://forum.babylonjs.com/)
+
+*If you are convinced that you found a bug, please use the following template for your issue:*
+
+**Repro**
+- Bug repro on [playground](https://playground.babylonjs.com):
+- Expected result:
+- Current result:
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Desktop (please complete the following information):**
+ - OS: [e.g. iOS]
+ - Browser [e.g. chrome, safari]
+ - Version [e.g. 22]
+
+**Smartphone (please complete the following information):**
+ - Device: [e.g. iPhone6]
+ - OS: [e.g. iOS8.1]
+ - Browser [e.g. stock browser, safari]
+ - Version [e.g. 22]
+
+**Additional context**
+Add any other context about the problem here.