Add GitHub issue template

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

.github/issue_template.md

@@ -0,0 +1,19 @@
+Please read Wiki carefully, especially https://github.com/shadowsocks/shadowsocks-windows/wiki/Troubleshooting.
+Please answer these questions before submitting your issue. Thanks!
+
+### Version(release version or AppVeyor link)
+
+
+### Environment(Operating system, .NET Framework, etc)
+
+
+### Steps you have tried
+
+
+### What did you expect to see?
+
+
+### What did you see instead?
+
+
+### Config and error log in detail (with all sensitive info masked)