[PathKit] Add docs page

No-Try: true
Docs-Preview: https://skia.org/?cl=147620
Bug: skia:8216
Change-Id: Iec5d1be49504b579bdc0893658941d3d722f676c
Reviewed-on: https://skia-review.googlesource.com/147620
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>

site/user/modules/pathkit.md

@@ -0,0 +1,29 @@
+PathKit - Skia in the Browser
+=============================
+
+Skia has made its [SkPath](../api/SkPath_Reference) object and many related methods
+available to JS clients (e.g. Web Browsers) using WebAssembly and asm.js.
+
+Download the library
+--------------------
+
+See [the npm page](https://www.npmjs.com/package/experimental-pathkit-wasm) for details on downloading
+and getting started.
+
+Features
+--------
+
+PathKit is still under rapid development, so the exact API is still changing.
+
+The primary features are:
+
+  - API compatibility (e.g. drop-in replacement) with [Path2D](https://developer.mozilla.org/en-US/docs/Web/API/Path2D)
+  - Can output to SVG / Canvas / Path2D
+  - Exposes a variety of path effects: <img width=800 src="./PathKit_effects.png"/>
+
+
+Example code
+------------
+The best place to look for examples on how to use PathKit would be in the
+[example.html](https://github.com/google/skia/blob/master/experimental/pathkit/npm-wasm/example.html#L45)
+which comes in the npm package.