github: add issue template

.github/ISSUE_TEMPLATE

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+Please answer these questions before submitting your issue. Thanks!
+
+1. What did you do?
+If possible, provide a recipe for reproducing the error.
+
+
+2. What did you expect to see?
+
+
+
+3. What did you see instead?
+
+
+
+4. What version of frp are you using (./frpc -v or ./frps -v)?