add ISSUE_TEMPLATE

Author: icymind

.github/ISSUE_TEMPLATE.md

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+Please answer these questions before submitting your issue. Thanks!
+
+(Please mention that if the issue you filed is solved, you may wish to close it by yourself. Thanks again.)
+
+(PS, you can remove 3 lines above, including this one, before post your issue.)
+
+### What version of VRouter are you using?
+
+
+### What operating system are you using?
+
+
+### What information shows in VRouter's "System" Tab?
+
+
+### What is the result of command `nslookup qq.com` When turnning on and off VRouter?
+
+
+### What is the result of command `traceroute 114.114.114.114`(macOS) `tracert 114.114.114.114`(Windows) when turnning on and off VRouter?
+
+
+### What are the contents of log? `tail -n 50 ~/Library/Application\ Support/vrouter/vrouter.log`(macOS), `Get-Content ~/AppData/Roaming/vrouter/vrouter.log  -tail 50 -Encoding UTF8`(Windows Powershell)