fixing README.md file to update pip install command

[towfeeqfayaz11]

This is fix for issue: #621

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: alwayslove2013, towfeeqfayaz11
To complete the pull request process, please assign xuanyang-cn after the PR has been reviewed.
You can assign the PR to them by writing /assign @xuanyang-cn in a comment when ready.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[alwayslove2013]

@towfeeqfayaz11 pip install vectordb-bench[pinecone] works in most cases. However, in some shells, the characters [ and ] are interpreted as wildcards, which can cause unexpected behavior. Adding quotes around it like pip install 'vectordb-bench[pinecone]', will prevent the shell from parsing those special characters and let pip handle them correctly instead.

Your change is really necessary and helpful. We truly appreciate your contribution to the project!