merge docs onto README

[rbenjos]

instructions are incomplete.
when trying to run
python Closure_Project/manage.py migrate
i'm getting the following exception:
No local .env or GOOGLE_CLOUD_PROJECT detected. No secrets found.

can we please make this step more clear? or address the following exception?

[ScDor]

do you have a valid .env file set up?

[rbenjos]

probably not, as it is not mentioned in the README (i think?)

[ghost]

It is written here:
https://github.com/ScDor/Closure/blob/master/docs/local_dev.md

But we should migrate the docs to the README. Will do.