[Docs] Move algorithm guide + exclude branding doc

[dsikka]

• Move adding a new algorithm guide to a new folder
• Exclude branding doc from readthedocs build

Sample build: https://vllm--285.org.readthedocs.build/projects/speculators/en/285/

[github-actions]

Summary

Status	Count
🔍 Total	162
✅ Successful	159
⏳ Timeouts	0
🔀 Redirected	2
👻 Excluded	0
❓ Unknown	0
🚫 Errors	1
⛔ Unsupported	0

Errors per input

Errors in docs/developer/index.md

• [ERROR] file:///home/runner/work/speculators/speculators/docs/developer/add_new_algorithms.md | Cannot find file: File not found. Check if file exists and path is correct

Redirects per input

Redirects in CONTRIBUTING.md

• [200] https://docs.pytest.org/ | Redirect: Followed 1 redirect resolving to the final status of: OK. Redirects: https://docs.pytest.org/ --> https://docs.pytest.org/en/stable/

Redirects in docs/developer/contributing.md

• [200] https://docs.pytest.org/ | Redirect: Followed 1 redirect resolving to the final status of: OK. Redirects: https://docs.pytest.org/ --> https://docs.pytest.org/en/stable/
  Full Github Actions output

[github-actions]

📦 Build Artifacts Available
The build artifacts (`.whl` and `.tar.gz`) have been successfully generated and are available for download: https://github.com/vllm-project/speculators/actions/runs/21876979782/artifacts/5453798295.
They will be retained for up to 30 days.
Commit: 414d4e1