Add client and cluster client config descriptions

Closes: #186

Author: nicktorwald

README.md

@@ -130,6 +130,51 @@ all the results, you could override this:
 protected void complete(TarantoolPacket packet, TarantoolOp<?> future);
 ```
 
+### Client config options
+
+The client configuration options are represented through the `TarantoolClientConfig` class.
+
+Supported options are follow:
+
+1. `username` is used to authenticate and authorize an user in a Taratool server instance.
+   Default value is `null` that means client will attempt to auth as a *guest*.
+2. `password` is used to authenticate an user in a Taratool server instance.
+   Default value is `null`.
+3. `defaultRequestSize` used to be an initial binary buffer size in bytes to send requests.
+   Default value is `4096` (4 KB).
+4. `predictedFutures` is used to initialize an initial capacity of hash map which stores
+   response futures. The client is asynchronous under the hood even though it provides
+   a synchronous operations using `java.concurrent.CompletableFuture`.
+   Default value is `(1024 * 1024) / 0.75) + 1`.
+5. `writerThreadPriority` describes a priority of writer thread.
+   Default value is `Thread.NORM_PRIORITY` (5).
+6. `readerThreadPriority` describes a priority of reader thread.
+   Default value is `Thread.NORM_PRIORITY` (5).
+7. `sharedBufferSize` sets a shared buffer size in bytes (place where client collects
+   requests when socket is busy on write).
+   Default value is `8 * 1024 * 1024` (8 MB).
+8. `directWriteFactor` is used as a factor to calculate a threshold whether
+   request will be accommodated in the shared buffer. If the request size exceeds
+   `directWriteFactor * sharedBufferSize` request is sent directly.
+   Defualt value is `0.5`.
+9. `writeTimeoutMillis` sets the max time in ms to perform writing and send the bytes.
+    Default value is 60 * 1000 (1 minute).
+10. `useNewCall` configures whether client has to use new *CALL* request signature or old
+    one used to be active in Tarantool 1.6.
+    Default value is `true`.
+11. `initTimeoutMilli` sets a max time in ms to establish connection to the server
+    Default values is `60 * 1000L` (1 minute).
+12. `connectionTimeout` is a hint and can be passed to the socket providers which
+    implement `ConfigurableSocketChannelProvider` interface. This hint should be
+    interpreter as a connection timeout in ms per attempt where `0` means no limit.
+    Default value is `2 * 1000` (2 seconds).
+13. `retryCount` is a hint and can be passed to the socket providers which
+    implement `ConfigurableSocketChannelProvider` interface. This hint should be
+    interpreter as a maximal number of attempts to connect to Tarantool instance.
+    Default value is `3`.  
+14. `operationExpiryTimeMillis` is a default request timeout in ms.
+    Default value is `1000` (1 second).
+
 ## Spring NamedParameterJdbcTemplate usage example
 
 The JDBC driver uses `TarantoolClient` implementation to provide a communication with server.
@@ -348,6 +393,20 @@ client.syncOps().insert(45, Arrays.asList(1, 1));
   The client does its best to catch the moment when there are no pending responses
   and perform a reconnection.  
 
+### Client config options
+
+In addition to the options for [the standard client](#client-config-options), cluster
+config provides some extra options:
+
+1. `executor` defines an executor that will be used as a thread of execution to retry writes.
+   Default values is `null` which means the cluster client will use *a single thread executor*.
+2. `clusterDiscoveryEntryFunction` is a name of the stored function to be used to fetch list of
+   instances.
+   Default value is `null` (not set).
+3. `clusterDiscoveryDelayMillis` describes how often in ms to poll the server for a new list of
+   cluster nodes.
+   Default value is `60 * 1000` (1 minute).
+
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