Add legal documentation

see: eclipsefdn/emo-team/emo#644 (closed)

Required files:

• License files in all repository roots
• README
• CONTRIBUTING (or equivalent)

Recommended files:

• NOTICES or equivalent (you can use the Legal Documentation generator available under committer tools)
• CODE_OF_CONDUCT
• SECURITY

See examples for Security file and Code of Conduct.

Required elements:

• ECA is referenced/described

Recommended elements:

• Security policy is described