MAINT: add GitHub issue template (#332)

Author: eigenfoo

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,21 @@
+## Problem Description
+
+**Please provide a minimal, self-contained, and reproducible example:**
+```python
+[Paste code here]
+```
+
+**Please provide the full traceback:**
+```python
+[Paste traceback here]
+```
+
+**Please provide any additional information below:**
+
+
+## Versions
+
+* Alphalens version: 
+* Python version: 
+* Pandas version: 
+* Matplotlib version: