feat: add diff viewer to tools (#563)

* Add diff viewer to tools

* Copy desc into body

* adjust wording

* capitalization

* Add source link

* Apply suggestions from code review

---------

Co-authored-by: Matouš Kučera <[email protected]>

Author: jpenilla

config/sidebar.misc.ts

@@ -25,6 +25,7 @@ const misc: SidebarsConfig = {
             "tools/start-script-gen",
             "tools/minimessage-web-editor",
             "tools/item-command-converter",
+            "tools/diff-viewer",
           ],
         },
         "java-install",

docs/misc/tools/diff-viewer.mdx

@@ -0,0 +1,20 @@
+---
+slug: /tools/diff-viewer
+description: Multi-file rich diff viewer for GitHub and diff/patch files.
+---
+
+# Diff Viewer
+
+Multi-file rich diff viewer with support for GitHub commits, PRs, and comparisons, as well as
+diff and patch files.
+The GitHub diff viewer is a great tool for most uses cases, but it has a variety of limitations,
+especially when dealing with large diffs where the viewer will perform poorly or even crash. The
+Patch Roulette diff viewer aims to solve this problem while also providing a variety of additional
+features useful for PaperMC and generally, such as special handling for second-order diffs. We have
+also built a browser extension for Firefox and Chrome to streamline opening GitHub diffs in the
+viewer.
+
+- https://patch-roulette.papermc.io/diff - The diff viewer itself
+- [Chrome Extension](https://chromewebstore.google.com/detail/patch-roulette/feaaoepdocmiibjilhoahgldkaajfnhb)
+- [Firefox Extension](https://addons.mozilla.org/en-US/firefox/addon/patch-roulette/)
+- https://github.com/PaperMC/patch-roulette - Patch Roulette GitHub repository