Update issue templates

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+#### For new checks and feature suggestions
+- [ ] https://www.shellcheck.net/ (i.e. the latest commit) currently gives no useful warnings about this
+- [ ] I searched through https://github.com/koalaman/shellcheck/issues and didn't find anything related
+
+#### Here's a snippet or screenshot that shows a potential problem:
+
+```sh
+#!/bin/sh
+your script here
+```
+
+#### Here's what shellcheck currently says:
+
+
+
+#### Here's what I wanted to see: