Add support for `Edit Post`

- [ ] Figure out how to edit a post since it isn't explained in the documentation
- [ ] Implement `update` method in `Posts` class
- [ ] Update `IPosts` accordingly
- [ ] Create Query and Response types (based on X Documentation)
- [ ] Update unit tests
- [ ] Update integration tests
- [ ] Update Readme
- [ ] Update list of supported endpoints
- [ ] Add example
- [ ] Update Table of contents

Start by reading the documentation referenced in the issue and inspecting the existing Posts class and IPosts interface. Identify the X API details needed for the update method, then review the current unit and integration tests before adding coverage. Done means the update types and implementation work, tests pass, and the README endpoint list, example, and table of contents are updated.

Written by the indexing model from the issue text.