Add issue template with code sandbox

Author: danbovey

.github/ISSUE_TEMPLATE/Bug_report.md

@@ -0,0 +1,22 @@
+---
+name: Bug report
+about: Submit a bug you found using the package
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Please clone your layout and use of react-infinite-scroller by forking [this Code Sandbox](https://codesandbox.io/s/my6vo3yo78) and linking it here. Doing so will massively expedite getting the bug fixed! 👊
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Device (please complete the following information):**
+ - OS: [e.g. Mac]
+ - Browser [e.g. chrome, safari]
+ - Version [e.g. 22]