[1.10.x] Edited multi-db topic guide for grammar and clarity.

Backport of ea65c7cb48 from master

docs/topics/db/multi-db.txt

@@ -45,11 +45,11 @@ If the concept of a ``default`` database doesn't make sense in the context
 of your project, you need to be careful to always specify the database
 that you want to use. Django requires that a ``default`` database entry
 be defined, but the parameters dictionary can be left blank if it will not be
-used. You must setup :setting:`DATABASE_ROUTERS` for all of your apps' models,
+used. To do this, you must set up :setting:`DATABASE_ROUTERS` for all of your
-including those in any contrib and third-party apps you are using, so that no
+apps' models, including those in any contrib and third-party apps you're using,
-queries are routed to the default database in order to do this. The following
+so that no queries are routed to the default database. The following is an
-is an example ``settings.py`` snippet defining two non-default databases, with
+example ``settings.py`` snippet defining two non-default databases, with the
-the ``default`` entry intentionally left empty::
+``default`` entry intentionally left empty::
 
     DATABASES = {
         'default': {},
@@ -78,7 +78,7 @@ The :djadmin:`migrate` management command operates on one database at a
 time. By default, it operates on the ``default`` database, but by
 providing the :option:`--database <migrate --database>` option, you can tell it
 to synchronize a different database. So, to synchronize all models onto
-all databases in our example, you would need to call::
+all databases in the first example above, you would need to call::
 
     $ ./manage.py migrate
     $ ./manage.py migrate --database=users
@@ -88,6 +88,13 @@ particular database, you can define a :ref:`database
 router<topics-db-multi-db-routing>` that implements a policy
 constraining the availability of particular models.
 
+If, as in the second example above, you've left the ``default`` database empty,
+you must provide a database name each time you run :djadmin:`migrate`. Omitting
+the database name would raise an error. For the second example::
+
+    $ ./manage.py migrate --database=users
+    $ ./manage.py migrate --database=customers
+
 Using other management commands
 -------------------------------
 
@@ -359,8 +366,8 @@ routers are defined)::
     DATABASE_ROUTERS = ['path.to.AuthRouter', 'path.to.PrimaryReplicaRouter']
 
 The order in which routers are processed is significant. Routers will
-be queried in the order the are listed in the
+be queried in the order they are listed in the
-:setting:`DATABASE_ROUTERS` setting . In this example, the
+:setting:`DATABASE_ROUTERS` setting. In this example, the
 ``AuthRouter`` is processed before the ``PrimaryReplicaRouter``, and as a
 result, decisions concerning the models in ``auth`` are processed
 before any other decision is made. If the :setting:`DATABASE_ROUTERS`
@@ -394,6 +401,13 @@ With this setup installed, lets run some Django code::
     >>> # ... but if we re-retrieve the object, it will come back on a replica
     >>> mh = Book.objects.get(title='Mostly Harmless')
 
+This example defined a router to handle interaction with models from the
+``auth`` app, and other routers to handle interaction with all other apps. If
+you left your ``default`` database empty and don't want to define a catch-all
+database router to handle all apps not otherwise specified, your routers must
+handle the names of all apps in :setting:`INSTALLED_APPS` before you migrate.
+See :ref:`contrib_app_multiple_databases` for information about contrib apps
+that must be together in one database.
 
 Manually selecting a database
 =============================
@@ -586,7 +600,8 @@ where all objects of a given type are stored on a specific database
 usage of multiple databases is more complex, your ``ModelAdmin`` will
 need to reflect that strategy.
 
-Inlines can be handled in a similar fashion. They require three customized methods::
+:class:`~django.contrib.admin.InlineModelAdmin` objects can be handled in a
+similar fashion. They require three customized methods::
 
     class MultiDBTabularInline(admin.TabularInline):
         using = 'other'