Added documents

docs/Assemble-context.md

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+# Assemble context API
+
+```kotlin
+public val CustomProtocolContext: ProtocolContextBuilder.() -> Unit = {
+    rsaEncryptor = RSA1024Encryptor { key, data -> ... }
+    sha1Hasher = Sha1Hasher { serverId, secretKey, publicKey -> ... }
+    cipherFactory = { key -> ... }
+    authProvider = AuthenticationProvider { url, accessToken, uuid, serverIdHash -> ... }
+    socketEngine = MyCustomTCPSocketImpl()
+}
+```
+
+> If using `DefaultProtocolContext` from `libmc-protocol-context` as the default context implementation,
+> please refer to [Implementing TCPSocket](Impl-TCP-Socket.md)
+
+# Modify exists context API implementation
+
+```kotlin
+fun main() {
+    val myNewProtocolContext = DefaultProtocolContext.withCustom {
+        rsaEncryptor = RSA1024Encryptor { key, data -> ... }
+        sha1Hasher = Sha1Hasher { serverId, secretKey, publicKey -> ... }
+        cipherFactory = { key -> ... }
+        authProvider = AuthenticationProvider { url, accessToken, uuid, serverIdHash -> ... }
+        socketEngine = MyCustomTCPSocketImpl()
+    }
+}
+```
+
+> Call `.withCustom` on a `ProtocolContextBuilder` to modify exists context implementation
+