Implement generation of README file for output repo

[luis261]

ideas for now:

• add shields.io badge, as a nice looking way of easily discerning repos automatically setup by aztra
• if feasible (and if I'm sure it won't leak anything in terms of Security), persist the config input the repo was generated with
• write creation date to README as well (as convenience feature, instead of having to look through git log/blame)

[luis261]

ready to be merged in principle, but still has to go through e2e testing. I'll try to remember to use this version the next time I use aztra to setup another project, if that runs fine, this can be de-drafted & merged