Update issue templates

Guide to use Gitea issues.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -7,6 +7,16 @@ assignees: ''
 
 ---
 
+<!--
+We would appreciated if you report a bug at our Gitea instance's issue page:
+https://git.joinplu.me/Plume/Plume/issues
+You can login to the Gitea with your GitHub account.
+
+We welcome to receive bug reports here, GitHub, too.
+-->
+
+
+
 <!-- Describe your bug, explaining how to reproduce it, and what was expected -->
 
 

.github/ISSUE_TEMPLATE/feature_request.md

@@ -7,6 +7,15 @@ assignees: ''
 
 ---
 
+<!--
+We would appreciated if you request a feature at our Gitea instance's issue page:
+https://git.joinplu.me/Plume/Plume/issues
+You can login to the Gitea with your GitHub account.
+
+We welcome to receive feature requests here, GitHub, too.
+-->
+
+
 **Is your feature request related to a problem? Please describe.**
 A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]