Add issue template

.github/issue_template.md

@@ -0,0 +1,18 @@
+Please answer these questions before submitting your issue. Thanks!
+
+### What version of shadowsocks-libev are you using?
+
+
+### What operating system are you using?
+
+
+### What did you do?
+
+
+### What did you expect to see?
+
+
+### What did you see instead?
+
+
+### What is your config in detail (with all sensitive info masked)?