feature #5319 [Console] Command Lifecycle explications (94noni)

This PR was squashed before being merged into the 2.3 branch (closes #5319).

Discussion
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[Console] Command Lifecycle explications

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3+
| Fixed tickets | #4996, #4366

Hi

I took the doc form https://github.com/symfony/symfony-demo/blob/master/src/AppBundle/Command/AddUserCommand.php by @javiereguiluz  as a minimal explanations for this, which IMO could be beneficial for devs

Commits
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f45c392 [Console] Command Lifecycle explications

components/console/introduction.rst

@@ -112,6 +112,31 @@ This prints::
 
     HELLO FABIEN
 
+Command Lifecycle
+~~~~~~~~~~~~~~~~~
+
+Commands have three lifecycle methods:
+
+:method:`Symfony\\Component\\Console\\Command\\Command::initialize`
+    This method is executed before the ``interact()`` and the ``execute()``
+    methods. It's main purpose is to initialize the variables used in the
+    rest of the command methods.
+
+:method:`Symfony\\Component\\Console\\Command\\Command::interact`
+    This method is executed after ``initialize()`` and before ``execute()``.
+    Its purpose is to check if some of the options/arguments are missing
+    and interactively ask the user for those values. This is the last place
+    where you can ask for missing options/arguments otherwise the command
+    will throw an error.
+
+:method:`Symfony\\Component\\Console\\Command\\Command::execute`
+    This method is executed after ``interact()`` and ``initialize()``.
+    It contains the logic you want the command executes.
+
+Note that ``execute()`` is the only required method of the three.
+
+The ``initialize()`` and ``interact()`` methods are completely optional.
+
 .. _components-console-coloring:
 
 Coloring the Output