[PATCH 3 of 4] docs: add documentation about internationalization from a user perspective

[Thomas De Schampheleire]

# HG changeset patch
# User Thomas De Schampheleire <thomas.de.schampheleire at gmail.com>
# Date 1497729099 -7200
#      Sat Jun 17 21:51:39 2017 +0200
# Node ID 5e8d981053e390d630fbeb867e8d61858f836cf1
# Parent  8c756862fd5ad0f775d8ba93c1a6ec1616fbc34a
docs: add documentation about internationalization from a user perspective

While there is already documentation about creating and updating
translations (developer perspective), there was nothing for the user/admin
of Kallithea.
Since the handling in TurboGears2 is different, this is a good time to add
it.

diff --git a/docs/setup.rst b/docs/setup.rst
--- a/docs/setup.rst
+++ b/docs/setup.rst
@@ -67,6 +67,19 @@ You are now ready to use Kallithea. To r
   repositories.
 
 
+Internationalization (i18n support)
+-----------------------------------
+The Kallithea web interface is automatically displayed in the user's
+preferred language, as indicated by the browser. Thus, different users may see
+the application in different languages. If the requested language is not
+available (because the translation file for that language does not yet exist or
+is incomplete), the language specified in setting ``i18n.lang`` in the Kallithea configuration file is used as fallback. If no fallback language is explicitly specified, English is used.
+
+If you want to disable automatic language detection and instead configure a
+fixed language regardless of user preference, set ``i18n.enabled = false`` and
+set ``i18n.lang`` to the desired language (or leave empty for English).
+
+
 Using Kallithea with SSH
 ------------------------