[doc] add installation instruction.

Author: makasim

Diff for: docs/amqp_transport.md

@@ -3,6 +3,7 @@
 Implements [AMQP specifications](https://www.rabbitmq.com/specification.html).
 Build on top of [php amqp extension](https://github.com/pdezwart/php-amqp).
 
+* [Installation](#installation)
 * [Create context](#create-context)
 * [Declare topic](#declare-topic)
 * [Declare queue](#decalre-queue)
@@ -12,6 +13,12 @@ Build on top of [php amqp extension](https://github.com/pdezwart/php-amqp).
 * [Consume message](#consume-message)
 * [Purge queue messages](#purge-queue-messages)
 
+## Installation
+
+```bash
+$ composer require enqueue/amqp-ext
+```
+
 ## Create context
 
 ```php

Diff for: docs/filesystem_transport.md

@@ -5,6 +5,7 @@ It creates a file per queue\topic.
 A message is a line inside the file.
 **Limitations** It works only in auto ack mode. Local by nature therefor messages are not visible on other servers.  
 
+* [Installation](#installation)
 * [Create context](#create-context)
 * [Declare topic](#declare-topic)
 * [Declare queue](#decalre-queue)
@@ -14,6 +15,12 @@ A message is a line inside the file.
 * [Consume message](#consume-message)
 * [Purge queue messages](#purge-queue-messages)
 
+## Installation
+
+```bash
+$ composer require enqueue/fs
+```
+
 ## Create context
 
 ```php

Diff for: docs/null_transport.md

@@ -4,6 +4,14 @@ This a special transport implementation, kind of stub.
 It does not send nor receive anything.
 Useful in tests for example.
 
+* [Installation](#installation)
+* [Create context](#create-context)
+
+## Installation
+
+```bash
+$ composer require enqueue/enqueue
+```
 
 ## Create context
 

Diff for: docs/stomp_transport.md

@@ -1,9 +1,17 @@
 # STOMP transport
 
+* [Installation](#installation)
+* [Create context](#create-context)
 * [Send message to topic](#send-message-to-topic)
 * [Send message to queue](#send-message-to-queue)
 * [Consume message](#consume-message)
 
+## Installation
+
+```bash
+$ composer require enqueue/stomp
+```
+
 ## Create context
 
 ```php