README install commands reference non-existent repo anthropics/claude-for-financial-services

## Bug

The README's install instructions reference a repository that doesn't exist on GitHub, so the very first install step fails for every
new user.

## Repro

```bash
$ claude plugin marketplace add anthropics/claude-for-financial-services
Adding marketplace…
✘ Failed to add marketplace: Failed to clone marketplace repository:
remote: Repository not found.
fatal: repository 'https://github.com/anthropics/claude-for-financial-services.git/' not found
```

## Root cause

The README mixes up two different names:

- **Repo slug** (what `marketplace add` clones): `anthropics/financial-services`
- **Marketplace name** (declared in `.claude-plugin/marketplace.json`, used in `plugin install ...@`):
`claude-for-financial-services`

The README uses the marketplace name in the `marketplace add` command, where the repo slug is required.

## Suggested fix

In `README.md`, under **Claude Code CLI**:

```diff
- claude plugin marketplace add anthropics/claude-for-financial-services
+ claude plugin marketplace add anthropics/financial-services
```

The subsequent `plugin install ...@claude-for-financial-services` lines are correct and should stay as-is, since they reference the
marketplace name.

Under **Cowork → Settings → Plugins → Add plugin**:

```diff
- Paste repo URL: `https://github.com/anthropics/claude-for-financial-services`
+ Paste repo URL: `https://github.com/anthropics/financial-services`
```

## Environment

- Claude Code CLI
- macOS (Darwin 25.4.0)