BOPE tutorial text edits (#1972)

Summary:
Pull Request resolved: #1972

## Motivation

Made a couple minor corrections to the BOPE tutorial, bringing the text in line with the code. The code and text probably drifted apart over time.

### Have you read the [Contributing Guidelines on pull requests](https://github.com/pytorch/botorch/blob/main/CONTRIBUTING.md#pull-requests)?

Yes

Pull Request resolved: #1971

Test Plan: Check that it renders okay in GH

Reviewed By: esantorella

Differential Revision: D48175913

Pulled By: saitcakmak

fbshipit-source-id: f312366955ffc69683b06c37ea971e595f1cf738