Add diff viewer to tools

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 +1,16 @@
+---
+slug: /tools/diff-viewer
+description: Multi-file rich diff viewer for GitHub and diff/patch files.
+---
+
+# Diff Viewer
+
+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 solves 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/)