feat: add readme (tokenlist-fetch.md)

Author: jcamor3s

tokenlist-fetch.md

@@ -0,0 +1,61 @@
+# Token List Fetch Feature
+
+Automated token list management with local and CI execution options.
+
+## Local Usage
+
+Run these commands in order:
+
+```bash
+# 1. Fetch token list from external source
+npm run tokenlist:fetch
+
+# 2. Generate token list files
+npm run generate
+
+# 3. Create PR with changes
+npm run tokenlist:pr
+```
+
+## CI Usage
+
+Use the GitHub Actions workflow:
+
+1. Go to **Actions** tab
+2. Select **"Token List Fetch"** workflow
+3. Configure inputs:
+   - `source_url`: External token list URL
+   - `target_token_file`: Local file path
+   - `assets_dir`: Logo storage directory
+4. Click **"Run workflow"**
+
+## Environment Variables
+
+| Variable            | Purpose                 | Default                                       |
+| ------------------- | ----------------------- | --------------------------------------------- |
+| `SOURCE_URL`        | External token list URL | -                                             |
+| `TARGET_TOKEN_FILE` | Local token file path   | `src/tokenlists/balancer/tokens/berachain.ts` |
+| `ASSETS_DIR`        | Logo assets directory   | `src/assets/images/tokens`                    |
+| `GITHUB_TOKEN`      | PR creation (CI only)   | -                                             |
+| `INFURA_KEY`        | Blockchain API access   | -                                             |
+| `ALCHEMY_KEY`       | Alternative API access  | -                                             |
+
+## Workflow Steps
+
+1. **Fetch**: Download token list and logos
+2. **Generate**: Process and format token data
+3. **Detect Changes**: Compare with existing files
+4. **Create PR**: If changes found, create pull request
+5. **Add Comment**: Include workflow metadata
+
+## Required Secrets (CI)
+
+- `GITHUB_TOKEN`: Repository access
+- `INFURA_KEY`: Blockchain API
+- `ALCHEMY_KEY`: Alternative API
+
+## Troubleshooting
+
+- **No changes detected**: Source data unchanged or wrong paths
+- **PR creation fails**: Check `GITHUB_TOKEN` secret
+- **Fetch fails**: Verify source URL accessibility