docs: fix Python package name in getting started

[suyua9]

📋 Description

• fix the Python install command in docs/getting-started.md
• align the getting-started guide with the published package metadata and the other README files, which already use openmemory-py

🔄 Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🎨 Style/UI changes
• ♻️ Code refactoring
• ⚡ Performance improvements
• 🧪 Test updates
• 🔧 Build/CI changes

🧪 Testing

• I have tested this change locally
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Validated by:

• checking packages/openmemory-py/pyproject.toml (name = "openmemory-py")
• verifying the remaining install snippets in README.md and packages/openmemory-py/README.md already use openmemory-py

📱 Screenshots (if applicable)

• not applicable

🔍 Code Review Checklist

• Code follows the project's coding standards
• Self-review of the code has been performed
• Code is properly commented, particularly in hard-to-understand areas
• Changes generate no new warnings
• Any dependent changes have been merged and published

📚 Related Issues

• none

🚀 Deployment Notes

• none; docs-only change

📋 Additional Context

• this avoids sending Python users to the unrelated openmemory package when following the getting-started guide

[nullure]

LGTM