[DOC] Fix documentation headers

[atrievel]

Summary

Replaced all instances of the ### RST headers with a standard format: ===

Fixes #232

List of changes proposed in this PR (pull-request)

• [x] Refactored docs/development/index.rst with new headers
• [x] Refactored docs/development/release_instructions.rst with new headers
• [x] Refactored docs/development/roadmap.rst with new headers
• [x] Ran tests via tox command
• [x] Added name to .zenodo.json contributor file

[atrievel]

@jdkent Awesome, thanks for allowing me to contribute!