Merge branch '2.3' into 2.6

* 2.3:
  Fixed some minor syntax issues.
  Reflect links correctly in gmail.rst
  Revisions to the gmail.rst doc
  Update gmail.rst
  Minor grammar fix.

Author: weaverryan

book/installation.rst

@@ -127,7 +127,7 @@ based on `Composer`_.
 
 Composer is the dependency manager used by modern PHP applications and it can
 also be used to create new applications based on the Symfony Framework. If you
-don't have installed it globally, start by reading the next section.
+don't have it installed globally, start by reading the next section.
 
 Installing Composer Globally
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

cookbook/email/gmail.rst

@@ -75,3 +75,13 @@ You're done!
 
     The ``gmail`` transport is simply a shortcut that uses the ``smtp`` transport
     and sets ``encryption``, ``auth_mode`` and ``host`` to work with Gmail.
+
+.. note::
+
+    Depending on your Gmail account settings, you may get authentication errors
+    within your app. If your Gmail account uses 2-Step-Verification, you should
+    `generate an App password`_ to use for your ``mailer_password`` parameter.
+    You should also ensure that you `allow less secure apps to access your Gmail account`_.
+
+.. _`generate an App password`: https://support.google.com/accounts/answer/185833
+.. _`allow less secure apps to access your Gmail account`: https://support.google.com/accounts/answer/6010255