docs: fix proof_getTransactionReceipt description

[peter941221]

Fixes #339

This PR aligns the proof namespace docs with the current RPC contract in src/Nethermind/Nethermind.JsonRpc/Modules/Proof/IProofRpcModule.cs.

Failure mechanism:

• proof_getTransactionReceipt was documented as if it behaved like eth_call and returned account/storage proofs.
• proof_getTransactionByHash was also misdescribed as returning the result of eth_getTransactionReceipt.
• Both sections documented blockHeader as unconditional even though it is gated by includeHeader.

Semantic change:

• proof_getTransactionByHash now matches the implemented behavior: eth_getTransactionByHash data plus a transaction inclusion proof against transactionsRoot, with optional RLP block header.
• proof_getTransactionReceipt now matches the implemented behavior: eth_getTransactionReceipt data plus transaction and receipt inclusion proofs against transactionsRoot and receiptsRoot, with optional RLP block header.
• blockHeader is now documented as optional in both response sections.

Preserved invariant:

• No runtime behavior changes; this is a docs-only correction to match the existing RPC interface metadata.

Testing:

• npm run build