docs: improve installation guide for clarity

[Omaima-Ameen]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

This PR improves the Installation section of the README by:

Improving formatting for readability

Adding a short usage snippet for Node environments

Clarifying that the package is ESM-only

This is a documentation-only change with no modifications to runtime code.

[Omaima-Ameen]

Hi! I noticed the CI failed, but my changes only modify the README and do not affect code or tests.
It looks like the failure might be unrelated.
Please let me know if anything is needed from my side!

[Murderlon]

The unified ecosystem consists of 300+ repositories and great care is taken to keep the readme's as consistent as possible. This deviates from that for, in my opinion, no gains. At this point it must be obvious that anyone who uses yarn/pnpm knows what to do when they find a readme that only showcases npm. As far as I know we don't keep track of which Vite/Webpack version we support so adding this just means signing up for the maintenance burden of tracking that too, and that's of course besides the fact that there are many more bundlers these days.