HTML comment to hide after line in README

[cxmeel]

Add the option to hide content in the README after a given line. This would ensure that only content between the <!--moonwave-hide-after-this-line--> and <!--moonwave-hide-before-this-line--> HTML comments is hidden.

While this might seem like a niche scenario, I prefer to use reference links in my markdown in project READMEs. This makes it easy to reuse a README with common links/images without having to adjust every reference to another project throughout the content.

Because moonwave hides all content before the HTML tag, including references, you end up with a README that looks like this:

Here's a partial raw README from Sift for reference:

<!-- Shields -->

[shields/github-release]: https://img.shields.io/github/v/release/csqrl/sift?label=latest+release&style=flat
[shields/wally]: https://img.shields.io/endpoint?url=https://runkit.io/clockworksquirrel/wally-version-shield/branches/master/csqrl/sift&color=blue&label=wally&style=flat
[shields/npm]: https://img.shields.io/npm/v/@rbxts/sift?style=flat

<!--moonwave-hide-after-this-line-->

# Sift

<!--moonwave-hide-before-this-line-->

<div align="center">

[![Source code][badges/github]][sift] [![NPM Package][badges/npm]][sift/npm] [![Itch.io store page][badges/itch]][sift/itch.io] [![Roblox library][badges/roblox]][sift/roblox]

[![Latest GitHub version][shields/github-release]][sift/releases] [![Latest Wally version][shields/wally]][sift/wally] [![Latest NPM version][shields/npm]][sift/npm]

</div>

Immutable data library for Luau and roblox-ts.