add introduction --> agent-oriented-development

[FelixNicolaeBucsa]

Proposed changes

Moved agent-oriented development section into new introduction.

Issues

Links to any issues resolved.

Types of changes

What types of changes does your code introduce to agents-aea? Put an x in the boxes that apply

• [ ] Bugfix (non-breaking change that fixes an issue)
• [ ] New feature (non-breaking change that adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to stop working as expected)
• [ ] Something else (e.g. test, package, script, example, deployment, infrastructure, ...)

Checklist

Put an x in the boxes that apply.

• [x] I have read the CONTRIBUTING document.
• [x] I have based my branch, and I am making a pull request against, the develop branch.
• [ ] Lint and unit tests pass locally with my changes.

If applicable

• [ ] I have added tests that prove my fix is effective or that my feature works.
• [ ] I have checked that code coverage does not decrease.
• [ ] I have added/updated the documentations.
• [ ] Dependent changes have been merged and published in downstream modules.

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did, what alternatives you considered, etc.