Fix a grammo

Change-Id: I0b9d21cc17772902343430d7a05b31d1f52785ed

docs/source/index.rst

diff --git a/docs/source/index.rst b/docs/source/index.rst
index 0111600..e34b707 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -17,7 +17,7 @@
 
 * Read the :ref:`chapter-tutorial`
 
-* Browse the :ref:`chapter-modeling` and :ref:`chapter-solving`
+* Browse the :ref:`chapter-modeling` API and :ref:`chapter-solving` API.
 
 * Join the `mailing list
   <https://groups.google.com/forum/?fromgroups#!forum/ceres-solver>`_

docs/source/introduction.rst

diff --git a/docs/source/introduction.rst b/docs/source/introduction.rst
index e6f65e5..19a6f2e 100644
--- a/docs/source/introduction.rst
+++ b/docs/source/introduction.rst
@@ -12,7 +12,7 @@
 
 **Features**
 
-#. A friendly :ref:`chapter-modeling`.
+#. A friendly :ref:`chapter-modeling` API.
 
 #. Automatic and numeric differentiation.