message: [cli] Add "Local Development" section to README
  Adds a section to the CLI readme explaining how to check out the source code and use `ts-eager` for local development.
diff: @@ -14,13 +14,13 @@ Vercel is the optimal workflow for frontend teams. All-in-one: Static and Jamsta
  To install the latest version of Vercel CLI, visit [vercel.com/download](https://vercel.com/download) or run this command:
  -```sh
  +```bash
  npm i -g vercel
  ```
  To quickly start a new project, run the following commands:
  -```
  +```bash
  vercel init # Pick an example project
  cd <PROJECT> # Change directory to the new project
  vercel # Deploy to the cloud
  @@ -29,3 +29,31 @@ vercel # Deploy to the cloud
  ## Documentation
  For details on how to use Vercel CLI, check out our [documentation](https://vercel.com/docs).
  +
  +## Local Development
  +
  +To develop Vercel CLI, first check out the source code, install dependencies, and build all packages:
  +
  +```bash
  +git clone https://github.com/vercel/vercel.git
  +cd vercel
  +yarn
  +yarn build
  +```
  +
  +At this point you can make modifications to the CLI source code and test them out locally. The CLI source code is located in the `packages/cli` directory.
  +
  +```bash
  +cd packages/cli
  +```
  +
  +From within the `packages/cli` directory, you can use the `ts-eager` command line tool to quickly excute Vercel CLI from its TypeScript source code directly (without having to manually compile first). For example:
  +
  +```bash
  +npx ts-eager src
  +npx ts-eager src login
  +npx ts-eager src switch --debug
  +npx ts-eager src dev
  +```
  +
  +When you are satisfied with your changes, make a commit and create a pull request!
  