[BUG] Outdated code examples in README

[drknzz]

What happened

The code examples in readme, showing the use of async and sync api:

• create Client instance which is now an abstract class
• do not use an account, making invoke throw an error

Probably the best solution would be to use only call and call_sync in the examples as they don't require an account.

Stack trace

Steps to reproduce

SDK Version

0.11.0-alpha

Python version

3.8.4

What operating system are you using?

Mac

Is there an existing issue for this?

• I have searched the existing issues and verified no issue exits for this problem.

[cptartur]

Where exactly this problem exists? We should probably fix it soon.

[drknzz]

There are only 2 examples in readme.

[drknzz]

I think code examples from readme should always work after a user copy pastes them into their ide. It should be somewhat of a check that the library has been installed successfully. For any further uses, they should go to the documentation web page.
Therefore we probably shouldn't be using an account there - just a pure GatewayClient and a method call.

[cptartur]

I see your point. We can do some improvements to readme.