Secret Manager doesn't tell me which parameters are required

Looking at this ol favorite:

```ts
const sm = new SecretManagerServiceClient();
const [secrets] = await sm.listSecrets({
parent: 'projects/el-gato',
});
```

Looking at the `listSecrets` method, I see it takes an options bag. Great! I dig deeper:

```ts
listSecrets(request: protos.google.cloud.secretmanager.v1.IListSecretsRequest, options?: gax.CallOptions): Promise<[protos.google.cloud.secretmanager.v1.ISecret[], protos.google.cloud.secretmanager.v1.IListSecretsRequest | null, protos.google.cloud.secretmanager.v1.IListSecretsResponse]>;
```

Ok, fine, what does `IListSecretsRequest` look like:

```ts
/** Properties of a ListSecretsRequest. */
interface IListSecretsRequest {

/** ListSecretsRequest parent */
parent?: (string|null);

/** ListSecretsRequest pageSize */
pageSize?: (number|null);

/** ListSecretsRequest pageToken */
pageToken?: (string|null);
}
```

This has 2 separate problems:

1. I have no idea which of these parameters are required. I know that when I ran my code without it, I got an exception for not passing a `parent` :)

2. I have no idea what any of these properties mean (I mean I do, but a mortal wouldn't). Aren't there better descriptions somewhere for these properties in the protos?