docs: fix grammatical errors in evaluation and self-hosting sections

[shardool-patil]

Summary

What changed?
Fixed minor grammatical errors in the README.md file.

Why was this change needed? / What problem does it solve?
It improves the readability and maintains the professional quality of the documentation.
Specific changes:

1. LLM Evaluation section: Corrected a typo ("or you custom evaluators" -> "or your custom evaluators").
2. Self-Hosting Agenta section: Corrected subject-verb agreement ("refers" -> "refer") and adjusted comma placement for better sentence flow.

Testing

Verified locally

Previewed the README.md Markdown locally to ensure no formatting or links were accidentally broken.

Added or updated tests

N/A (Documentation update only)

QA follow-up

N/A

Demo

N/A

Checklist

• I have included a video or screen recording for UI changes, or marked Demo as N/A
• Relevant tests pass locally
• Relevant linting and formatting pass locally
• I have signed the CLA, or I will sign it when the bot prompts me

Contributor Resources

• Contributing guide
• Creating your first PR
• Development mode
• Testing
• Formatting and linting
• Slack support

[vercel]

@shardool-patil is attempting to deploy a commit to the agenta projects Team on Vercel.

A member of the Team first needs to authorize it.

[CLAassistant]

All committers have signed the CLA.

[mmabrouk]

Thanks @shardool-patil !