minor #19561 [Console] Fix indentation of Help: section of txt usage help (okdana)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #19561).

Discussion
----------

[Console] Fix indentation of Help: section of txt usage help

| Q             | A
| ------------- | ---
| Branch?       | 3.1
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

I noticed that all of the sections output by `TextDescriptor` (*Usage*, *Arguments*, *Options*, *Available commands*, &c.) are indented by 2 spaces, except for the *Help* section, which is indented by only 1 space:

<img width="1039" alt="screen shot 2016-08-07 at 08 53 53" src="https://cloud.githubusercontent.com/assets/122095/17462818/34c99cfc-5c7e-11e6-9674-9324c537fc01.png">

This PR makes the indentation consistent with the other sections. (I don't *think* that qualifies as a BC break?)

Commits
-------

4e4c674 Console: Fix indentation of Help: section of txt usage help

src/Symfony/Component/Console/Descriptor/TextDescriptor.php

@@ -156,7 +156,7 @@ class TextDescriptor extends Descriptor
             $this->writeText("\n");
             $this->writeText('<comment>Help:</comment>', $options);
             $this->writeText("\n");
-            $this->writeText(' '.str_replace("\n", "\n ", $help), $options);
+            $this->writeText('  '.str_replace("\n", "\n  ", $help), $options);
             $this->writeText("\n");
         }
     }

src/Symfony/Component/Console/Tests/Fixtures/application_run2.txt

@@ -18,12 +18,12 @@ Options:
   -v|vv|vvv, --verbose  Increase the verbosity of messages: 1 for normal output, 2 for more verbose output and 3 for debug
 
 Help:
- The help command displays help for a given command:
- 
-   php app/console help list
- 
- You can also output the help in other formats by using the --format option:
- 
-   php app/console help --format=xml list
- 
- To display the list of available commands, please use the list command.
+  The help command displays help for a given command:
+  
+    php app/console help list
+  
+  You can also output the help in other formats by using the --format option:
+  
+    php app/console help --format=xml list
+  
+  To display the list of available commands, please use the list command.

src/Symfony/Component/Console/Tests/Fixtures/application_run3.txt

@@ -10,18 +10,18 @@ Options:
       --format=FORMAT  The output format (txt, xml, json, or md) [default: "txt"]
 
 Help:
- The list command lists all commands:
- 
-   php app/console list
- 
- You can also display the commands for a specific namespace:
- 
-   php app/console list test
- 
- You can also output the information in other formats by using the --format option:
- 
-   php app/console list --format=xml
- 
- It's also possible to get raw list of commands (useful for embedding command runner):
- 
-   php app/console list --raw
+  The list command lists all commands:
+  
+    php app/console list
+  
+  You can also display the commands for a specific namespace:
+  
+    php app/console list test
+  
+  You can also output the information in other formats by using the --format option:
+  
+    php app/console list --format=xml
+  
+  It's also possible to get raw list of commands (useful for embedding command runner):
+  
+    php app/console list --raw

src/Symfony/Component/Console/Tests/Fixtures/command_1.txt

@@ -4,4 +4,4 @@
   alias2
 
 <comment>Help:</comment>
- command 1 help
+  command 1 help

src/Symfony/Component/Console/Tests/Fixtures/command_2.txt

@@ -10,4 +10,4 @@
   <info>-o, --option_name</info>  
 
 <comment>Help:</comment>
- command 2 help
+  command 2 help

src/Symfony/Component/Console/Tests/Fixtures/command_astext.txt

@@ -15,4 +15,4 @@
   <info>-v|vv|vvv, --verbose</info>  Increase the verbosity of messages: 1 for normal output, 2 for more verbose output and 3 for debug
 
 <comment>Help:</comment>
- help
+  help