bug #4342 Reworded a misleading Doctrine explanation (javiereguiluz)

This PR was merged into the 2.3 branch.

Discussion
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Reworded a misleading Doctrine explanation

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #4337

Commits
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ef86b52 Fixed typo
fef57d5 Reworded a misleading Doctrine explanation

book/doctrine.rst

@@ -544,13 +544,12 @@ Take a look at the previous example in more detail:
 
 .. note::
 
-  In fact, since Doctrine is aware of all your managed entities, when you
-  call the ``flush()`` method, it calculates an overall changeset and executes
-  the most efficient query/queries possible. For example, if you persist a
-  total of 100 ``Product`` objects and then subsequently call ``flush()``,
-  Doctrine will create a *single* prepared statement and re-use it for each
-  insert. This pattern is called *Unit of Work*, and it's used because it's
-  fast and efficient.
+  In fact, since Doctrine is aware of all your managed entities, when you call
+  the ``flush()`` method, it calculates an overall changeset and executes
+  the queries in the correct order. It utilizes cached prepared statement to
+  slightly improve the performance. For example, if you persist a total of 100
+  ``Product`` objects and then subsequently call ``flush()``, Doctrine will
+  execute 100 ``INSERT`` queries using a single prepared statement object.
 
 When creating or updating objects, the workflow is always the same. In the
 next section, you'll see how Doctrine is smart enough to automatically issue