minor #1595 Tweak warning message to point to #1593, asking for help (GBeushausen)

This PR was squashed before being merged into the 2.2.x-dev branch (closes #1595).

Discussion
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Tweak warning message to point to #1593, asking for help

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75585384 Tweak warning message to point to #1593, asking for help

README.rst

@@ -3,6 +3,8 @@ Silex, a simple Web Framework
 
 **WARNING**: Silex is in maintenance mode only. Ends of life is set to June
 2018. Read more on `Symfony's blog <http://symfony.com/blog/the-end-of-silex>`_.
+But Silex can be saved! Any **help** to keep Silex alive is greatly appreciated.
+See `#1593 <https://github.com/silexphp/Silex/issues/1593>`_.
 
 Silex is a PHP micro-framework to develop websites based on `Symfony
 components`_: