Link to direct pricing information from readme

Hello. I'm looking into using this project for client side error reporting and wanted to assess the GCP costs of using it.

Looking at the GCP Error Reporting costs here: https://cloud.google.com/stackdriver/pricing#error-report-costs
```
For the current pricing information, see [Error Reporting Pricing](https://cloud.google.com/error-reporting#pricing).

For limits that apply to your use of Error Reporting, see [Quotas and limits](https://cloud.google.com/error-reporting/quotas).
```

The first link seems promising and links to here: https://cloud.google.com/error-reporting#pricing
```
Pricing
Error Reporting supports errors sent through the use of either:

[Cloud Logging](https://cloud.google.com/logging/), which, for pricing purposes, measures the quantity of log data loaded and processed by Logging or other Google Cloud services. See [Pricing](https://cloud.google.com/stackdriver/pricing) for details.
[Error Reporting API](https://cloud.google.com/error-reporting/reference/): you might incur minor Cloud Logging costs if your errors are ingested by Logging. For details, go to [Report error events](https://cloud.google.com/error-reporting/reference#operations).
```
This is where I get a little lost. Does this project make use of Cloud Logging? If so then the "Cloud Logging pricing summary" at this link should indicate accurate costs I think? https://cloud.google.com/stackdriver/pricing

From the sounds of the readme of this project, it feels like the "Error Reporting API" would more likely be the correct option. The 2 links under that option both go to the same page (https://cloud.google.com/error-reporting/reference/) and it doesn't mention pricing.

Because of the above, I am unable to assess the costs of using `stackdriver-errors-js` in my project.