Add validator client readme

validator_client/README.md

@@ -0,0 +1,67 @@
+# Lighthouse Validator Client
+
+The Validator Client (VC) is a stand-alone binary which connects to a Beacon
+Node (BN) and fulfils the roles of a validator.
+
+## Roles
+
+The VC is responsible for the following tasks:
+
+- Requesting validator duties (a.k.a. shuffling) from the BN.
+- Prompting the BN to produce a new block, when a validators block production
+	duties require.
+- Completing all the fields on a new block (e.g., RANDAO reveal, signature) and
+	publishing the block to a BN.
+- Prompting the BN to produce a new shard atteststation as per a validators
+	duties.
+- Ensuring that no slashable messages are signed by a validator private key.
+- Keeping track of the system clock and how it relates to slots/epochs.
+
+The VC is capable of managing multiple validators in the same process tree.
+
+## Implementation
+
+_This section describes the present implementation of this VC binary._
+
+### Services
+
+Each validator is represented by two services, one which tracks the validator
+duties and another which performs block production duties.
+
+A separate thread is maintained for each service, for each validator. As such,
+a single validator utilises three (3) threads (one for the base VC and two for
+each service) and two validators utilise five (5) threads.
+
+#### `DutiesManagerService`
+
+Polls a BN and requests validator responsibilities, as well as a validator
+index. The outcome of a successful poll is a `EpochDuties` struct:
+
+```rust
+EpochDuties {
+	validator_index: u64,
+	block_prodcution_slot: u64,
+}
+```
+
+This is stored in the `EpochDutiesMap`, a `HashMap` mapping `epoch ->
+EpochDuties`.
+
+#### `BlockProducerService`
+
+Polls the system clock and determines if a block needs to be produced. Reads
+from the `EpochDutiesMap` maintained by the `DutiesManagerService`.
+
+If block production is required, performs all the necessary duties to request,
+complete and return a block from the BN.
+
+### Configuration
+
+Presently the validator specifics (pubkey, etc.) are randomly generated and the
+chain specification (slot length, BLS domain, etc.) are fixed to foundation
+parameters. This is temporary and will be upgrade so these parameters can be
+read from file (or initialized on first-boot).
+
+## BN Communication
+
+The VC communicates with the BN via a gRPC/protobuf connection.