Improve PEcAn.SIPNET README and documentation structure

[sujalkurkute]

Description

This PR improves the PEcAn.SIPNET README to provide clearer, more structured, and user-friendly documentation.

Changes include:

• Added a concise overview of SIPNET and its integration with PEcAn
• Improved the "What is SIPNET?" section with clearer and more focused content
• Added a "Using SIPNET via PEcAn" section with links to tutorials and documentation
• Introduced a "Documentation Structure" section to clarify the relationship between README, SIPNET docs, and PEcAn documentation
• Simplified installation instructions and removed redundant details
• Replaced plain URLs with properly formatted Markdown links

Motivation and Context

The existing SIPNET documentation was fragmented and contained generic/template content. This update improves clarity, removes duplication, and provides better navigation between README, PEcAn documentation, and SIPNET standalone docs.

Fixes: #3703

Review Time Estimate

• When possible

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• My change requires a change to the documentation.
• My name is in the list of CITATION.cff
• I agree that PEcAn Project may distribute my contribution under any or all of
  • the same license as the existing code,
  • and/or the BSD 3-clause license.
• I have updated the CHANGELOG.md.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[omkarrr2533]

Hey @sujalkurkute, welcome and thanks for the PR! 🙌

Just a heads up PR #3705 was already merged on March 7 and covered most of what's here (What is SIPNET, installation updates, demo links etc). Your changes might conflict with or revert some of that work.
Also worth knowing PR #3880 is still open and tackles the same issue more broadly.

The Documentation Structure section you added is a nice touch that isn't in either of those PRs though!

Would suggest rebasing on develop first and then seeing what still makes sense to keep. Happy to help if you have questions! 👍

[sujalkurkute]

Thanks @omkarrr2533 for the feedback!

I’ll rebase my branch on develop and remove the duplicate changes that are already covered in PR #3705. I’ll keep and refine the documentation structure section.

Appreciate your guidance!

[sujalkurkute]

Thanks for the feedback!

I have rebased my branch, removed the duplicate content, and kept only the documentation structure section. Please let me know if any further changes are needed.