Remove nesting option from playground, update docs

On by default!

README.md

@@ -25,7 +25,7 @@ An extremely fast CSS parser, transformer, and minifier written in Rust. Use it
 - **Vendor prefixing** – Lightning CSS accepts a list of browser targets, and automatically adds (and removes) vendor prefixes.
 - **Browserslist configuration** – Lightning CSS supports opt-in browserslist configuration discovery to resolve browser targets and integrate with your existing tools and config setup.
 - **Syntax lowering** – Lightning CSS parses modern CSS syntax, and generates more compatible output where needed, based on browser targets.
-  - CSS Nesting (draft spec)
+  - CSS Nesting
   - Custom media queries (draft spec)
   - Logical properties
   * [Color Level 5](https://drafts.csswg.org/css-color-5/)

website/pages/transpilation.md

@@ -436,7 +436,7 @@ p:not(:first-child, .lead) {
 compiles to:
 
 ```css
-p:not(:is(:first-child, (.lead)) {
+p:not(:is(:first-child, .lead)) {
   margin-top: 1em;
 }
 ```

website/playground/index.html

@@ -170,7 +170,6 @@ <h3>Options</h3>
         <label><input id="analyzeDependencies" type="checkbox"> Analyze dependencies</label>
         <label><input id="visitorEnabled" type="checkbox"> Visitor</label>
         <h3>Draft syntax</h3>
-        <label><input id="nesting" type="checkbox" checked> Nesting</label>
         <label><input id="customMedia" type="checkbox" checked> Custom media queries</label>
         <h3>Targets</h3>
         <div class="targets">

website/playground/playground.js

@@ -46,7 +46,6 @@ function loadPlaygroundState() {
   } catch {
     return {
       minify: minify.checked,
-      nesting: nesting.checked,
       visitorEnabled: visitorEnabled.checked,
       targets: getTargets(),
       include: 0,
@@ -102,10 +101,6 @@ function reflectPlaygroundState(playgroundState) {
     compiledDependencies.hidden = !playgroundState.analyzeDependencies;
   }
 
-  if (typeof playgroundState.nesting !== 'undefined') {
-    nesting.checked = playgroundState.nesting;
-  }
-
   if (typeof playgroundState.customMedia !== 'undefined') {
     customMedia.checked = playgroundState.customMedia;
   }
@@ -144,7 +139,6 @@ function savePlaygroundState() {
   let data = new FormData(sidebar);
   const playgroundState = {
     minify: minify.checked,
-    nesting: nesting.checked,
     customMedia: customMedia.checked,
     cssModules: cssModules.checked,
     analyzeDependencies: analyzeDependencies.checked,
@@ -216,7 +210,6 @@ function update() {
       include,
       exclude,
       drafts: {
-        nesting: nesting.checked,
         customMedia: customMedia.checked
       },
       cssModules: cssModules.checked,