push: improve 'no remote specified hint

[jorgeorpinel]

More context around https://discordapp.com/channels/485586884165107732/563406153334128681/666010834702696450

$ dvc version
DVC version: 0.80.0
Python version: 3.7.6
Platform: Darwin-19.0.0-x86_64-i386-64bit
Binary: False
Package: brew

$ dvc init --no-scm
...
$ dvc push
ERROR: failed to push data to the cloud - config file error: no remote specified. Setup default remote with
    dvc config core.remote <name>
or use:
    dvc push -r <name>



Having any troubles? Hit us up at https://dvc.org/support, we are always happy to help!

• ✅ config file error: no remote specified: OK, this is the problem.
• ❌ Setup default remote with... or use...: Oops, actually I haven't even setup a remote. Maybe the hint should be different in this case?
• ❓ There 3 new lines between the hint and Having any troubles? ...

[jorgeorpinel]

May also affect other sync commands (pull, fetch).

[fabiosantoscode]

Picked this up and added a PR!