minor symfony#9182 Documented the PhpExecutableFinder utility (javiereguiluz)

This PR was squashed before being merged into the 2.7 branch (closes symfony#9182).

Discussion
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Documented the PhpExecutableFinder utility

I was going to document symfony#9003 ... but I think we should not explain that because it's an internal detail and the code can be changed/improved at any time and we cannot keep the docs in sync. However, we could document the PhpExecutableFinder utility if we decide is useful enough.

Commits
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cbd6e2b Documented the PhpExecutableFinder utility

Author: javiereguiluz

components/process.rst

@@ -350,6 +350,19 @@ Use :method:`Symfony\\Component\\Process\\Process::disableOutput` and
     Moreover, you could not pass a callback to the ``start()``, ``run()`` or ``mustRun()``
     methods or use ``setIdleTimeout()``.
 
+Finding the Executable PHP Binary
+---------------------------------
+
+This component also provides a utility class called
+:class:`Symfony\\Component\\Process\\PhpExecutableFinder` which returns the
+absolute path of the executable PHP binary available on your server::
+
+    use Symfony\Component\Process\PhpExecutableFinder;
+
+    $phpBinaryFinder = new PhpExecutableFinder();
+    $phpBinaryPath = $phpBinaryFinder->find();
+    // $phpBinaryPath = '/usr/local/bin/php' (the result will be different on your computer)
+
 .. _`Symfony Issue#5759`: https://github.com/symfony/symfony/issues/5759
 .. _`PHP Bug#39992`: https://bugs.php.net/bug.php?id=39992
 .. _`exec`: https://en.wikipedia.org/wiki/Exec_(operating_system)