docs: update consensus state docs

docs/ibc/light-clients/consensus-state.md

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+# Implementing the `ConsensusState` interface
+
+A `ConsensusState` is the snapshot of the counterparty chain that an IBC client uses to verify proofs (e.g. a block). The further development of multiple types of IBC light clients and the difficulties presented by this generalization problem (see [ADR-006](https://github.com/cosmos/ibc-go/blob/main/docs/architecture/adr-006-02-client-refactor.md) for more information about this historical context) led to the design decision of each client keeping track of and set its own `ClientState` and `ConsensusState`, as well as the simplification of client `ConsensusState` updates through the generalized `ClientMessage` interface.
+
+The below [`ConsensusState`](https://github.com/cosmos/ibc-go/blob/main/modules/core/exported/client.go#L134) interface is a generalized interface for the types of information a `ConsensusState` could contain. For a reference `ConsensusState` implementation, please see the [Tendermint light client `ConsensusState`](https://github.com/cosmos/ibc-go/blob/main/modules/light-clients/07-tendermint/consensus_state.go).
+
+## `ClientType` method
+
+This is the type of client consensus. It should be the same as the `ClientType` return value for the [corresponding `ClientState` implementation](./client-state.md).
+
+## `GetTimestamp` method
+
+`GetTimestamp` should return the timestamp (in nanoseconds) of the consensus state snapshot.
+
+## `ValidateBasic` method
+
+`ValidateBasic` should validate every consensus state field and should return an error if any value is invalid. The light client implementer is in charge of determining which checks are required.

docs/ibc/light-clients/proofs.md

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docs/ibc/light-clients/update.md

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+# Implementing the `ClientMessage` interface
+
+As mentioned before in the documentation about [implementing the `ConsensusState` interface](./consensus-state.md), [`ClientMessage`](https://github.com/cosmos/ibc-go/blob/main/modules/core/exported/client.go#L145) is an interface used to update an IBC client. This update may be done by a single header, a batch of headers, misbehaviour, or any type which when verified produces a change to the consensus state of the IBC client. This interface has been purposefully kept generic in order to give the maximum amount of flexibility to the light client implementer. 
+
+```golang 
+type ClientMessage interface {
+	proto.Message
+
+	ClientType() string
+	ValidateBasic() error
+}
+```
+
+The `ClientMessage` will be passed to the client to be used in [`UpdateClient`](https://github.com/cosmos/ibc-go/blob/57da75a70145409247e85365b64a4b2fc6ddad2f/modules/core/02-client/keeper/client.go#L53), which will handle a number of cases including misbehaviour and/or updating the consensus state. However, this `UpdateClient` function will always reference the specific functions determined by the relevant `ClientState`. This is because `UpdateClient` retrieves the client state by client ID (available in `MsgUpdateClient`). This client state implements the `ClientState` interface for a specific client type (e.g. Tendermint). The functions called on the client state instance in `UpdateClient` will be the specific implementations of `VerifyClientMessage`, `CheckForMisbehaviour`, `UpdateStateOnMisbehaviour` and `UpdateState` functions of the `ClientState` interface for that particular client type.