docs: get_user_credentials doc to update no longer existing settings.

[C0t300]

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Fixes #286

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[sai-sunder-s]

It could be a Desktop/Installed application type as well.

Maybe just remove the application type part from the comment.

[C0t300]

I couldn't get it to work with Desktop/Installed Application, that's the main reason I submitted this pr.
Also I think the application type part is useful for newbies like me.

[sai-sunder-s]

What is the error you are running into for Desktop OAuth Client? I ran the below code and got a refresh token successfully. The client id and secret I used were of a Desktop Client.

import google_auth_oauthlib
from google.auth.transport.requests import Request

# TODO: Create a client ID for your project.
client_id = "<replace with client id>"
client_secret = "<replace with client secret>"
# TODO: Choose the needed scopes for your applications.
scopes = ["https://www.googleapis.com/auth/cloud-platform"]
cred = google_auth_oauthlib.get_user_credentials(
    scopes, client_id, client_secret
)

cred.refresh(Request())
print(cred.refresh_token)