docs: refresh official bip39 package metadata

[Luzijano]

Summary

• updates package metadata from the original contributor fork to the official BitgesellOfficial/bitgesell-bip39 repository
• makes the package description Bitgesell-specific instead of Bitcoin-specific
• fixes the README browserify example to reference bitgesell-bip39
• normalizes the BitcoinJS name in the attribution

Validation

• npm test -- --runInBand (383 tests passing)
• git diff --check

Bounty / improvement program

Submitted as a small docs/package metadata cleanup under BitgesellOfficial/bitgesell#81.

Assisted by Hermes Agent.

[MyTH-zyxeon]

Maintainer-facing review assist for the Bitgesell #81 improvement-program queue:

I rechecked this PR at head 5f0eaccaef9fc6bcda7d1785d97136c66fe67911. It is a small metadata/docs cleanup across README.md and package.json, currently OPEN/MERGEABLE/CLEAN, with no prior PR comments or reviews.

Suggested acceptance checks before merge:

• confirm the npm package name is intended to remain bitgesell-bip39 and that the README browserify example should use -r bitgesell-bip39 -s bip39 rather than preserving the upstream bip39 module alias;
• verify the package.json repository URL matches the canonical public repo and package publication plan;
• keep the Bitgesell-specific description if maintainers want this fork discoverable as a Bitgesell package rather than a generic Bitcoin BIP39 fork;
• decide whether the attribution typo fix (BitcoinJs -> BitcoinJS) should also add a trailing newline in a follow-up, since this patch preserves the no-newline marker;
• treat this under #81 as package-metadata/onboarding polish, not runtime wallet/key-generation logic.

The PR body reports npm test -- --runInBand with 383 tests passing and git diff --check; the main merge gate is package naming/publication intent, not code behavior.