Add clean-state tests

packages/typescript-typings/README.md

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+## @0xproject/typescript-typings
+
+Type repository for external packages used by 0x. This is like our small version of [DefinitelyTyped](https://github.com/DefinitelyTyped/DefinitelyTyped)
+
+## Installation
+
+```bash
+yarn add -D @0xproject/typescript-typings
+```
+
+## Usage
+
+Add the following line within an `compilerOptions` section of your `tsconfig.json`
+
+```json
+"typeRoots": ["node_modules/@0xproject/typescript-typings/types", "node_modules/@types"]
+```
+
+This will allow the TS compiler to first look into that repo and then fallback to DT types.
+
+## Contributing
+
+We strongly encourage that the community help us make improvements and determine the future direction of the protocol. To report bugs within this package, please create an issue in this repository.
+
+Please read our [contribution guidelines](../../CONTRIBUTING.md) before getting started.
+
+### Install Dependencies
+
+If you don't have yarn workspaces enabled (Yarn < v1.0) - enable them:
+
+```bash
+yarn config set workspaces-experimental true
+```
+
+Then install dependencies
+
+```bash
+yarn install
+```
+
+### Lint
+
+```bash
+yarn lint
+```