docs: add watch mode documentation

aider/website/docs/usage/watch.md

@@ -0,0 +1,49 @@
+---
+title: Aider in your IDE
+#highlight_image: /assets/browser.jpg
+parent: Usage
+nav_order: 750
+description: Aider can run in your browser, not just on the command line.
+---
+
+# Aider in your IDE
+
+If you run aider with `--watch-files`,
+it will watch all files in your repo for edits. If you edit a file and add comments with "AI instructions", aider will follow them. So you can put aider messages right into your source files, nearby the code they refer to. 
+
+
+Specifically, aider will react to one-liner comments (# ... or // ...) that either start or end with `AI` or `AI!`. 
+
+Comments that use `AI!` with an exclamation point are special. They trigger aider to take action to process all the AI comments and use them as instructions to make code changes.
+
+For example, if you included this AI comment in your code:
+
+```js
+function factorial(n)
+// Implement this. AI!
+```
+
+Then aider would update the file and implement the function:
+
+```js
+function factorial(n) {
+  if (n === 0 || n === 1) {
+    return 1;
+  } else {
+    return n * factorial(n - 1);
+  }
+}
+```
+
+This makes it easier to use aider from within your favorite editor or IDE. 
+See the demo video above of aider working with AI comments in VSCode.
+
+This capability is quite flexible and powerful once you get familiar with the various ways it can be used:
+
+- Just add #AI to a file to add it to the chat.
+- Add an AI comment in the function you want changed, explaining the change request in-context.
+  - `# Add error handling... AI!`
+- Drop multiple AI comments (in multiple files) before triggering aider with a final AI!:
+  - `# AI: Refactor this function...`
+  - `# ... into a method here in this class. AI!`
+