Issue templates: Rename bug report to documentation issue

Author: fhammerschmidt

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,9 @@
+---
+name: 🚨 Documentation issue
+about: Create an issue to help us improve the rescript-lang.org documentation website
+title: ''
+labels: ''
+assignees: ''
+
+---
+