minor symfony#4356 Remove incoherence between Doctrine and Propel introduction paragraphs (arnaugm)

This PR was merged into the 2.3 branch.

Discussion
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Remove incoherence between Doctrine and Propel introduction paragraphs

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | symfony#4349

The introductory paragraph of Doctrine and Propel sections, although both are true in some way, look contradictory, so a rephrase of at least one of the two paragraphs would be convenient.

Commits
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7992fdf Remove incoherence between Doctrine and Propel introduction paragraphs

Author: weaverryan

book/doctrine.rst

@@ -5,11 +5,13 @@ Databases and Doctrine
 ======================
 
 One of the most common and challenging tasks for any application
-involves persisting and reading information to and from a database. Fortunately,
-Symfony comes integrated with `Doctrine`_, a library whose sole goal is to
-give you powerful tools to make this easy. In this chapter, you'll learn the
-basic philosophy behind Doctrine and see how easy working with a database can
-be.
+involves persisting and reading information to and from a database. Although
+the Symfony full-stack framework doesn't integrate any ORM by default,
+the Symfony Standard Edition, which is the most widely used distribution,
+comes integrated with `Doctrine`_, a library whose sole goal is to give
+you powerful tools to make this easy. In this chapter, you'll learn the
+basic philosophy behind Doctrine and see how easy working with a database
+can be.
 
 .. note::