Add FAQ link to Issue template (#14020)

Author: 6543

.github/issue_template.md

@@ -2,10 +2,11 @@
 
 <!--
     1. Please speak English, this is the language all maintainers can speak and write.
-    2. Please ask questions or configuration/deploy problems on our Discord 
+    2. Please ask questions or configuration/deploy problems on our Discord
        server (https://discord.gg/gitea) or forum (https://discourse.gitea.io).
     3. Please take a moment to check that your issue doesn't already exist.
-    4. Please give all relevant information below for bug reports, because 
+    4. Make sure it's not mentioned in the FAQ (https://docs.gitea.io/en-us/faq)
+    5. Please give all relevant information below for bug reports, because
        incomplete details will be handled as an invalid report.
 -->