docs: add npm README and MIT license

[coffeexcoin]

Adds package documentation and licensing for the @abstract-foundation/mpp npm package.

• README.md: covers install, payment flow overview, charge vs session methods, server/client usage examples, exports, chain constants, paymaster and smart wallet support.
• LICENSE: MIT license, copyright Abstract Foundation.
• package.json: added license: "MIT" field and included LICENSE in files array for publishing.

[changeset-bot]

🦋 Changeset detected

Latest commit: 27e5789

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@abstract-foundation/mpp	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
mpp-abstract-mpp-demo	Ready	Preview, Comment	Mar 25, 2026 11:15pm

[cursor]

PR Summary

Low Risk
Low risk: documentation/licensing additions plus minor package.json metadata changes that only affect npm packaging/publishing.

Overview
Adds npm-facing documentation and licensing for @abstract-foundation/mpp.

Introduces a new README.md with install/usage and protocol details, adds an MIT LICENSE, and updates package.json to declare license: "MIT" and include LICENSE in the published files set. Includes a changeset for a patch release.

^{Written by Cursor Bugbot for commit 27e5789. This will update automatically on new commits. Configure here.}