[Feature request] Adding README.md for all connectors like Grafana-connector

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/iotdb/issues) and found nothing similar.

### Motivation

While exploring the `iotdb-extras repository`, I noticed that the `grafana-connector` module has a `README.md` providing clear documentation on installation, usage, and configuration. However the other connector modules do not have equivalent module-level documentation. Developers and contributors landing on these modules have no quick reference for understanding their purpose, architecture, configuration, or usage without diving directly into the source code. Standardizing README documentation across all connector modules would improve contributor onboarding, reduce friction for new users, and bring consistency to the repository.

### Solution

Add a `README.md` to each of the connector modules, following the same structure and style as the existing `grafana-connector` README:
Each README will cover module overview, prerequisites, build and installation instructions, basic usage examples, and configuration parameters — consistent with the existing `grafana-connector` documentation style.

### Alternatives

_No response_

### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!