delete the Dockerfile-55 file and rename Dockerfile-56 to Dockerfile-5

Since 5.5 and 5.6 dockerfiles are identical execept the base image php version.
Will let the users switch the php 5.6 and 5.5 version from the Dockerfile-5 by changing one char
in the first line. Removing this duplication will make contribution and maintance easier and faster.

README.md

@@ -659,20 +659,18 @@ The PHP-CLI extensions should be installed in `workspace/Dockerfile`.
 
 <br>
 <a name="Change-the-PHP-FPM-Version"></a>
-### Change the PHP-FPM Version
+### Change the (PHP-FPM) Version
 By default **PHP-FPM 7.0** is running.
 
 >The PHP-FPM is responsible of serving your application code, you don't have to change the PHP-CLI version if you are planing to run your application on different PHP-FPM version.
 
+#### A) Switch from PHP `7.0` to PHP `5.6`
+
 1 - Open the `docker-compose.yml`.
 
 2 - Search for `Dockerfile-70` in the PHP container section.
 
-3 - Change the version number.
-<br>
-Example to select version 5.6 instead of 7.0 you have to replace `Dockerfile-70` with `Dockerfile-56`.
-
-Sample:
+3 - Change the version number, by replacing `Dockerfile-70` with `Dockerfile-5`, like this:
 
 ```txt
 php-fpm:
@@ -681,19 +679,35 @@ php-fpm:
         dockerfile: Dockerfile-70
 ```
 
-Supported Versions:
-
-- For (PHP 7.0.*) use `Dockerfile-70`
-- For (PHP 5.6.*) use `Dockerfile-56`
-- For (PHP 5.5.*) use `Dockerfile-55`
-
-
 4 - Finally rebuild the container
 
 ```bash
 docker-compose build php
 ```
 
+#### B) Switch from PHP `7.0` or `5.6` to PHP `5.5`
+
+1 - Follow the steps of (Switch from PHP `7.0` to PHP `5.6`) except the last one "rebuilding container".
+
+2 - Open the `docker-compose.yml` again and make sure you are using `Dockerfile-5` like this:
+
+```txt
+php-fpm:
+    build:
+        context: ./php-fpm
+        dockerfile: Dockerfile-5
+```
+
+3 - Open `php-fpm/Dockerfile-5` file and on the first line replace the PHP version from (`FROM php:5.6-fpm`) to (`FROM php:5.5-fpm`).
+
+4 - Now you can rebuild the container
+
+```bash
+docker-compose build php
+```
+
+<br>
+
 For more details about the PHP base image, visit the [official PHP docker images](https://hub.docker.com/_/php/).