Update documentation on how to get access_token?

[Cobertos]

It seems like access_token is needed, and requires an implicit OAuth 2.0 flow (or that seems the easiest). I get xtackapi.stackapi.StackAPIError: ('https://api.stackexchange.com/2.2/sites/?pagesize=1000&page=1&filter=xxx&key=xxx&access_token=asdf', 403, 'access_denied', 'keyis not valid for passedaccess_token, token not found (does not exist).') without it

I ended up:

• Having to enable Enable Client Side OAuth Flow
• Creating a link like https://stackoverflow.com/oauth/dialog?client_id=[client_id]&scope=private_info,no_expiry&redirect_uri=https://stackexchange.com according to the auth docs
• Getting the access_token from the return hash in the browser

It's verbose to add all of that to the README.md, but may be nice to specify you'll have to manually do the OAuth 2.0 flow yourself. Either in browser or Insomnia or something

[karlicoss]

Ah, whoops! I had this snippet in my secrets.py file

# https://stackapps.com/apps/oauth/view/16169
# TODO move that to stexport instead?
def get_token():
    from subprocess import check_call
    from urllib.parse import urlencode
    # https://api.stackexchange.com/docs/authentication
    qs = [
        ('client_id'   , client_id),
        ('redirect_uri', redirect_uri),
        # https://api.stackexchange.com/docs/authentication#scope
        ('scope'       , 'private_info no_expiry')
    ]
    url = 'https://stackoverflow.com/oauth/dialog?' + urlencode(qs)
    check_call(['xdg-open', url])
    print("Now copy acces_token and put it in the script")


if __name__ == '__main__':
    get_token()

I guess makes sense to implement --login mode or something, similar to instapexport, for example: https://github.com/karlicoss/instapexport#setting-up