Merge pull request #341 from beauby/issue-template

Add template for issues.

.github/ISSUE_TEMPLATE.md

+# Summary
+
+<!-- Facebook has a bounty program for the safe disclosure of security bugs. In
+those cases, please go through the process outlined on that page and do not
+file a public issue. -->
+
+# Platform
+
+OS: <!-- e.g. macOS 10.13.3 -->
+
+Faiss version: <!-- git commit, e.g. 56383610bcb982d6591e2e2bea3516cb7723e04a -->
+
+Faiss compilation options: <!-- e.g. using MKL with compile flags ... -->
+
+Running on :
+- [ ] CPU
+- [ ] GPU
+
+# Reproduction instructions
+
+<!-- Please provide specific and comprehensive instructions to reproduce the
+described behavior. -->