Document what are the steps required for a validator to be included on-chain

[boulder225]

Problem to be solved

Validators need to know the steps required to be included on-chain, but this information is not currently documented in the Obol Network documentation.

Proposed solution

Add a new section to the Obol Network documentation titled "Steps for Validators to be Included On-Chain" that outlines the necessary steps for validators to be included on-chain. This section should include the following steps:

1. Validators must first submit an attestation to the network.
2. The attestation must be picked up by one of the aggregators for that attestation.
3. The aggregate is then broadcasted and picked up by a block builder.
4. The attestation is counted as "included" when the aggregation is included in a block.

We should include it under the FAQ and errors section.