Create a new python example script - submit_and_read_block

[mp-v2]

As per feedback, this PR has been redone to point to the iota-sdk repo, here: iotaledger/iota-sdk#230

Description of change

Existing examples are not fully-emcompassing. This example script aims to give the user a full picture of what they are doing and why.

This script has three steps:

1. Prepare the payload for a block
2. Submit the block to the Shimmer test network
3. Use the block ID to read the payload back from the network

It also provides the url to click and go to the explorer.

Type of change

• Documentation Fix

How the change has been tested

Ran it in terminal, it outputs what is expected.

Change checklist

Tick the boxes that are relevant to your changes, and delete any items that are not.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing unit tests pass locally with my changes