Improve README (#145)

This adds some info to the README.

Author: therve

README.md

@@ -18,9 +18,45 @@ npm install @datadog/datadog-api-client
 yarn add @datadog/datadog-api-client
 ```
 
-## Usage
+## Getting Started
 
-TBD
+Here's an example getting a monitor:
+
+```typescript
+import { v1 } from 'datadog-api-client';
+import * as fs from 'fs';
+
+const configuration = v1.createConfiguration();
+const apiInstance = new v1.MonitorsApi(configuration);
+
+let params:v1.MonitorsApiGetMonitorRequest = {
+  // number | The ID of the monitor
+  monitorId: 1,
+  // string | When specified, shows additional information about the group states. Choose one or more from `all`, `alert`, `warn`, and `no data`. (optional)
+  groupStates: "group_states_example",
+};
+
+apiInstance.getMonitor(params).then((data:any) => {
+  console.log('API called successfully. Returned data: ' + data);
+}).catch((error:any) => console.error(error));
+
+```
+
+## Documentation
+
+Documentation for API endpoints can be found under the docs subdirectories, in [v1](/docs/v1/)
+and [v2](/docs/v2/).
+
+## Contributing
+
+As most of the code in this repository is generated, we will only accept PRs for files
+that are not modified by our code-generation machinery (changes to the generated files
+would get overwritten). We happily accept contributions to files that are not autogenerated,
+such as tests and development tooling.
+
+## Author
+
+[email protected]
 
 ## License