DOCS: Add release notes for v0.4.0 release

[HarshCasper]

Changes introduced in this PR:

• Add release notes for the v0.4.0 release

Types of changes

What types of changes does your PR introduce?

Put an x in the boxes that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Documentation

Does your contribution include breaking changes or deprecations?
If so have you updated the documentation?

• Yes, docstrings
• Yes, main documentation
• Yes, deprecation notices