Fixes#452
When the empty state is rendered with a non-textual element (which it turns out all our current empty states are, because they have a `<button />` component as a call to action), this noisy error log was showing up in the `console`:
```
Warning: validateDOMNesting(...): <div> cannot appear as a descendant of <p>.
at div
at div
at p
at Typography (webpack-internal:///./node_modules/@material-ui/core/esm/Typography/Typography.js:166:28)
at WithStyles (webpack-internal:///./node_modules/@material-ui/styles/esm/withStyles/withStyles.js:64:31)
at div
at StyledComponent (webpack-internal:///./node_modules/@material-ui/styles/esm/styled/styled.js:95:28)
at EmptyState (webpack-internal:///./src/components/EmptyState/index.tsx:47:25)
...
at ProjectsPage (webpack-internal:///./src/pages/projects/index.tsx:37:18)
at Routes (webpack-internal:///./node_modules/react-router/index.js:275:5)
at ThemeProvider (webpack-internal:///./node_modules/@material-ui/styles/esm/ThemeProvider/ThemeProvider.js:44:24)
at UserProvider (webpack-internal:///./src/contexts/UserContext.tsx:100:55)
at SWRConfig$1 (webpack-internal:///./node_modules/swr/dist/index.esm.js:501:23)
at Router (webpack-internal:///./node_modules/react-router/index.js:209:15)
at BrowserRouter (webpack-internal:///./node_modules/react-router-dom/index.js:118:5)
at App
```
The issue was that the `description` prop could either be a `string` or an actual `React` component, but was always rendered as a child of a `<Typography />` component. The `<Typography>` component internally renders as a `<p>`, which is not valid to nest `<div>`s inside.
The fix is to not nest inside a `<Typography />` block, but an actual `<div />`.
This refactoring re-organizes the `site` folder to have a nested `src` folder.
Originally, [we wanted to keep the directory structure shallow](https://github.com/coder/coder/pull/8#issuecomment-1009578910) - but there were two points that motivated this change to introduce the `src` level.
1. We have several non-`src` folders now (`e2e`, `static`, `html_templates`, `.storybook`)
2. Having a `src` folder makes it easier to run XState Typegen
So given those two data points - I believe it makes sense to revisit that and introduce a `src` folder.
Kayla Washburn