Fix example that leads to error if copy-pasted

[nik-418]

Checklist

• [x] I've tested my changes.
• [x] I've read the Contribution Guidelines.
• [x] I've updated the documentation if necessary.

Motivation and Context

Minimizes developer frustration from error inherent in documentation.

Description

Just adds a missing ) in Readme 😄

[CaliCastle]

Thanks for noticing that parenthesis there!