[Process] add docs for ExecutableFinder

Author: dunglas

components/process.rst

@@ -483,10 +483,32 @@ Use :method:`Symfony\\Component\\Process\\Process::disableOutput` and
     However, it is possible to pass a callback to the ``start``, ``run`` or ``mustRun``
     methods to handle process output in a streaming fashion.
 
+
+Finding an Executable
+---------------------
+
+The Process Component component provides a utility class called
+:class:`Symfony\\Component\\Process\\ExecutableFinder` which finds
+and returns the absolute path of an executable::
+
+    use Symfony\Component\Process\ExecutableFinder;
+
+    $executableFinder = new ExecutableFinder();
+    $chromedriverPath = $executableFinder->find('chromedriver');
+    // $chromedriverPath = '/usr/local/bin/chromedriver' (the result will be different on your computer)
+
+The :method:`Symfony\Component\Process\ExecutableFinder::find` method also takes extra parameters to specify a default value
+to return and extra directories where to look for the executable::
+
+    use Symfony\Component\Process\ExecutableFinder;
+
+    $executableFinder = new ExecutableFinder();
+    $chromedriverPath = $executableFinder->find('chromedriver', '/path/to/chromedriver', ['local-bin/']);
+
 Finding the Executable PHP Binary
 ---------------------------------
 
-This component also provides a utility class called
+This component also provides a special utility class called
 :class:`Symfony\\Component\\Process\\PhpExecutableFinder` which returns the
 absolute path of the executable PHP binary available on your server::