Improve overview.rst with narrative and Quick Start example

[Monier-Ayman]

PR Description

This PR improves the overview.rst documentation file.

It:

• Adds a clearer narrative description of radiospectra
• Lists supported instruments with official names
• Adds a verified Quick Start example for e-CALLISTO
• Explains the workflow in plain English

Closes #85

AI Assistance Disclosure

AI tools were used for:

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding
• No AI tools were used

Regardless of AI use, the human contributor remains fully responsible for correctness, design choices, licensing compatibility, and long-term maintainability.

[Monier-Ayman]

Hi @samaloney, I wanted to give you an overview of what I’ve done in this PR (#165):

• Improved the Overview section of the documentation (overview.rst) for clarity and readability.
• Added a Quick Start example for e-CALLISTO using the public Spectrogram API.
• Listed all supported instruments with their official names.
• Explained the workflow in plain English for new users.
• Added a changelog entry and fixed it to match the PR number.
• Ensured the changelog has the final newline for pre-commit CI checks.

This should make it easier for new users to get started with radiospectra and for reviewers to verify the changes.

[samaloney]

Thanks for the PR just a few housekeeping issues please retain and use the PR template which is created when the PR is opened. (You can see it here: https://github.com/sunpy/.github/blob/main/.github/PULL_REQUEST_TEMPLATE.md)

[Monier-Ayman]

Thanks for the PR just a few housekeeping issues please retain and use the PR template which is created when the PR is opened. (You can see it here: https://github.com/sunpy/.github/blob/main/.github/PULL_REQUEST_TEMPLATE.md)

@samaloney
Thanks for the guidance. I have updated the PR description to follow the template.