Issue Template: Missing or Incorrect Documentation

1st chunk of `.github/ISSUE_TEMPLATE/missing_documentation.md`

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---
name: Missing or incorrect documentation
about: Help us improve the reference manual
title: ''
labels: documentation
assignees: ''

---

## Problem

<!-- describe your problem -->

## Proposal

<!-- propose a solution -->

## Checklist

<!-- make sure this issue is not redundant or obsolete -->

- [ ] checked [latest Nix manual] \([source])
- [ ] checked [open documentation issues and pull requests] for possible duplicates


---

Add :+1: to [issues you find important](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc).

Title: Issue Template: Missing or Incorrect Documentation

Summary

This is an issue template for reporting missing or incorrect documentation in the Nix reference manual. It includes sections for describing the problem, proposing a solution, and a checklist to ensure the issue is not redundant. It also encourages users to upvote important issues.