Improve installation documentation

[bibhas2]

Describe the feature or improvement you're requesting

There are two ways to install evals, From Git repo and from pip repository. I found the documentation super confusing as to when to use which approach. I think the README.md can be made clear as follows.

• Describe the two alternatives for installation.
• Then state: If you will be using one of the pre-build evaluations then use the "pip install" approach. If you wish to create your own evaluation then use the Git repo approach.

In fact, changing the sentence:

If you don't want to contribute new evals, but simply want to run them locally, you can install the evals package via pip:

To:

If you don't want to write your own evals and use one of the pre-built ones, you can install the evals package via pip:

Will do the job. I do not wish to contribute but write my own evals.

Additional context

No response

[Yash8745]

This makes sense. I also thought I could make custom evals even if I used pip install. The wording is confusing.