Improved the description of the issue templates (#554)

.github/ISSUE_TEMPLATE/custom.md

@@ -1,6 +1,6 @@
 ---
 name: Custom
-about: Open an issue in the repo that is neither a bug or a feature
+about: Open an issue in the repo that is neither a bug or a feature, such a new idea
 title: ''
 labels: ''
 assignees: ''

.github/ISSUE_TEMPLATE/feature_request.md

@@ -1,6 +1,6 @@
 ---
 name: "\U0001F680 Feature request"
-about: Suggest an idea for this project
+about: Suggest a new ECMAScript feature to be implemented, or a new capability of the engine.
 title: ''
 labels: enhancement
 assignees: ''