phrase translation provider

- added some documentation about the phrase translation provider

Author: wickedOne

translation.rst

@@ -603,6 +603,7 @@ Provider              Install with
 Crowdin               ``composer require symfony/crowdin-translation-provider``
 Loco (localise.biz)   ``composer require symfony/loco-translation-provider``
 Lokalise              ``composer require symfony/lokalise-translation-provider``
+Phrase                ``composer require symfony/phrase-translation-provider``
 ====================  ===========================================================
 
 Each library includes a :ref:`Symfony Flex recipe <symfony-flex>` that will add
@@ -692,6 +693,11 @@ configure the ``providers`` option:
             ],
         ]);
 
+.. important::
+
+    If you use Phrase as a provider you must configure a user agent in your dsn. See
+    `Identification via User-Agent`_ for reasoning and some examples.
+
 .. tip::
 
     If you use Lokalise as a provider and a locale format following the `ISO
@@ -701,6 +707,12 @@ configure the ``providers`` option:
     capital letters that specifies the national variety (e.g. "GB" or "US"
     according to `ISO 3166-1 alpha-2`_)).
 
+.. tip::
+
+    The Phrase provider uses Phrase's tag feature to map translations to Symfony's translation
+    domains. If you need some assistance with organising your tags in Phrase, you might want
+    to consider the `Phrase Tag Bundle`_ which provides some commands helping you with that.
+
 Pushing and Pulling Translations
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -1364,3 +1376,5 @@ Learn more
 .. _`Machine object format`: https://www.gnu.org/software/gettext/manual/html_node/MO-Files.html
 .. _`QT Translations TS XML`: https://doc.qt.io/qt-5/linguist-ts-file-format.html
 .. _`GitHub Actions`: https://docs.github.com/en/free-pro-team@latest/actions
+.. _`Identification via User-Agent`: https://developers.phrase.com/api/#overview--identification-via-user-agent
+.. _`Phrase Tag Bundle`: https://github.com/wickedOne/phrase-tag-bundle