message: Add client config builder readme
diff: -TODO
  \ No newline at end of file
  +# PolywrapClient Config Builder
  +
  +A DSL for building the PolywrapClient config object.
  +
  +Supports building configs using method chaining or imperatively.
  +
  +```typescript=
  +const config = new ClientConfigBuilder()
  + .add({
  + envs: [/*...*/],
  + interfaces: [/*...*/],
  + plugins: [/*...*/],
  + redirects: [/*...*/],
  + uriResolvers: [/*...*/],
  + })
  + .add({/*...*/})
  + .build();
  +
  +// ...
  +
  +const builder = new ClientConfigBuilder();
  +
  +builder.addDefaults();
  +
  +builder.add({
  + plugins: [/*...*/]
  +});
  +
  +builder.add({
  + envs: [/*...*/]
  +});
  +
  +const config = builder.build();
  +
  +
  +// ...
  +
  +let client = new PolywrapClient(config);
  +```
  +
  +## Methods
  +
  +The config builder currently supports 3 methods:
  +
  +#### `add(config: Partial<ClientConfig>)`
  +Appends each property of the supplied config object to the corresponding array of the builder's config.
  +
  +#### `addDefaults()`
  +Adds the `defaultClientConfig` object.
  +
  +#### `build()`
  +Returns a sanitized config object from the builder's config.
  