Better docs with step to step tutorial on how to set-up petitions

README can be improved with a speciffic guide on how to proceed and adding the relevant links to all the resources needed to set up a petition and understand the theoretical basis behind it.

Relevant links

App repo --> https://github.com/DECODEproject/decode-app/tree/master/docs
Web explaining decode tools --> https://tools.decodeproject.eu/
App web --> https://tools.decodeproject.eu/app/
Bcnnow web --> https://bcnnow.decodeprojec.eu
Bcnnow repo --> https://github.com/DECODEproject/bcnnow
Credential issuer in action --> https://credentials-zenroom10.decodeproject.eu/docs
Credential issuer repo --> https://github.com/DECODEproject/credential-issuer
Petitions API --> https://petitions-zenroom10.decodeproject.eu/docs
Petitions API repo --> https://github.com/DECODEproject/dddc-petition-api
Blockchain connector API --> https://github.com/DECODEproject/petition-tp-python