Add discourse link to issue template (go-gitea#74)

Author: cez81

.github/issue_template.md

@@ -1,5 +1,5 @@
 1. Please speak English, this is the language everybody of us can speak and write.
-2. Please ask questions or config/deploy problems on our Discord server: https://discord.gg/NsatcWJ
+2. Please ask questions or configuration/deploy problems on our Discord server (https://discord.gg/NsatcWJ) or forum (https://discourse.gitea.io).
 3. Please take a moment to search that an issue doesn't already exist.
 4. Please give all relevant information below for bug reports, incomplete details will be handled as an invalid report.