docs: usage on readme

Author: gnlow

README.md

@@ -1,2 +1,63 @@
 # lilgpu
 Lil wrapper to toy with WebGPU
+
+## Usage
+See [examples](/example/).
+
+### Browser
+```js
+import { initCanvas, d } from "https://esm.sh/gh/gnlow/lilgpu/browser.ts"
+
+const g = await initCanvas({
+    vertShader: `
+        @vertex
+        fn vs_main(@builtin(vertex_index) in_vertex_index: u32) -> @builtin(position) vec4<f32> {
+            let x = f32(i32(in_vertex_index) - 1);
+            let y = f32(i32(in_vertex_index & 1u) * 2 - 1);
+            return vec4<f32>(x, y, 0.0, 1.0);
+        }
+    `,
+    fragShader: `
+        @fragment
+        fn fs_main() -> @location(0) vec4<f32> {
+            return vec4<f32>(1.0, 0.0, 0.0, 1.0);
+        }
+    `,
+    canvas: document.querySelector("canvas"),
+})
+
+g.draw(3)
+```
+
+### Deno
+```ts
+import { initDeno } from "https://esm.sh/gh/gnlow/lilgpu/deno.ts"
+
+const g = await initDeno({
+    vertShader: `
+        @vertex
+        fn vs_main(@builtin(vertex_index) in_vertex_index: u32) -> @builtin(position) vec4<f32> {
+            let x = f32(i32(in_vertex_index) - 1);
+            let y = f32(i32(in_vertex_index & 1u) * 2 - 1);
+            return vec4<f32>(x, y, 0.0, 1.0);
+        }
+    `,
+    fragShader: `
+        @fragment
+        fn fs_main() -> @location(0) vec4<f32> {
+            return vec4<f32>(1.0, 0.0, 0.0, 1.0);
+        }
+    `,
+    width: 200,
+    height: 200,
+})
+
+g.draw(3)
+
+await Deno.writeFile("./triangle.png", await g.getImage())
+```
+
+#### Jupyter
+```ts
+await g.getImage() // Uint8Array
+```