Update README branding and documentation badge

[Irozuku]

Summary

Updates the README.rst to align with the project's current branding by replacing all occurrences of "DashAI" with "dashAI". The pull request also updates the documentation badge link to point to the new documentation website.

---

Type of Change

Check all that apply like this [x]:

• Backend change
• Frontend change
• CI / Workflow change
• Build / Packaging change
• Bug fix
• Documentation

---

Changes (by file)

• README.rst:

  • Replaced all instances of "DashAI" with "dashAI" to ensure consistent branding throughout the documentation.
  • Updated the documentation badge URL to point to https://docs.dash-ai.com/ instead of the previous ReadTheDocs site.
  • Updated references to the project name across headings, descriptions, installation instructions, examples, and other user facing documentation content.