feat(docs): Add extra information on the email dev seciton of the cli page

Author: gabrielmfern

apps/docs/cli.mdx

@@ -10,7 +10,63 @@ icon: 'square-terminal'
 
 Starts a local development server that will watch your files and automatically rebuild your email when you make changes.
 
-**Options**
+### Where can I place my static files for previewing
+
+Almost always you will need to have static files in your emails, and seeing
+them on the preview server without having to first host on a CDN is very helpful.
+
+We do allow for this, and currently, you can place your files inside of a `static` 
+directory inside of your `emails` directory. 
+
+This does adjust to your `--dir` option, so if your `emails` directory was inside
+of `./src/emails`, you would place your static files inside of `./src/emails/static`.
+
+These static files are directly served from our preview server by looking into the
+requests made into that end with `/static` and serving the files at that point,
+this also allows for you to have images inside of your emails like so:
+
+```jsx
+export default Email(props) {
+  return (
+    <div>
+      <img src="/static/email-logo.png" />
+    </div>
+  )
+}
+```
+
+### How to make the preview server ignore directories
+
+Once the preview server has started and is now open on `localhost`, the preview server
+reads recursively down into all of your files and directories. This can be disabled
+from a directory down by prefixing it with `_`, e.g. `components -> _components`. So if you wanted
+to make components for your emails, you could make a structure as follows:
+
+```bash
+my-project
+├── emails
+│   ├── _components
+│   │   └── this-is-not-going-to-appear-in-the-sidebar.tsx
+│   ├── email.tsx
+│   └── static
+├── package.json
+└── tsconfig.json
+```
+
+### The heuristics for files to be considered emails
+
+To avoid uncanny files appearing in the sidebar of the preview server,
+we account for two heuristics to determine weather or not we should
+include it:
+
+1. If file has `.js, .jsx or .tsx` file extensions
+2. If the file contains a `export default` expression by matching with the regex <br/>
+`/\bexport\s*default\b/gm`
+
+These can certainly fail as they are only heuristics, so if you do find
+any issues with these, feel free to open an [issue](https://github.com/resend/react-email/issues).
+
+### Options
 
 <ResponseField name="--dir" type="string" default="emails">
   Change the directory of your email templates.