docs: update root readme and add readme @repo/ui

packages/ui/README.md

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+# @repo/ui
+
+Shared UI components for frontend use. This package has already been set up with dummy **React UI library** (`<CounterButton>` and `<Link>` components) and **shadcn/ui** components (`<Button>` and `<Card>`).
+
+## What's inside?
+
+This repo includes the following packages and apps:
+
+### Apps and Packages
+
+- `tailwindcss`: Tailwind CSS configuration for styling
+- `postcss`: PostCSS configuration for processing CSS
+- `shadcn/ui`: shadcn/ui components for UI
+
+### Building and Running
+
+Building the UI will require exporting the components in the `package.json` file.
+
+For `Vite` apps, `vite-tsconfig-paths` package is required to ensure the UI components are properly built and available for use.
+
+For `Next.js` apps, the `next.config.ts` file needs to have `transpilePackages: ["@repo/ui"]` to ensure the UI components are properly built and available for use.
+
+Although not required, adding:
+
+```
+"paths": {
+	"@repo/ui/*": ["../../packages/ui/src/*"]
+}
+```
+
+in the `tsconfig.json` file of **each app** can help with TypeScript path resolution during development.
+
+### More Information
+
+#### [shadcn/ui](https://ui.shadcn.com/docs/monorepo) for UI components
+
+To use the CLI, run `npx shadcn@latest add <component-name>` in the `@repo/ui` package directory.
+
+It can also be run at each app directory and the CLI will automatically install `@radix-ui/react-slot` add the components to the shared `@repo/ui` package. Each app will need its own `components.json` file and the `paths` in the `tsconfig.json` file should be updated accordingly.
+
+#### [Tailwind CSS v4](https://tailwindcss.com/) for styling and to use shadcn/ui
+
+Each app needs its own `tailwind.config.js`file and `postcss.config.js` file but they all extend from the shared `@repo/ui/tailwind.config.js` and `@repo/ui/postcss.config.js` files.