Fixing minor typo

Changed "primary" to "primarily" in first paragraph.

Author: kwshaw1

README.rst

@@ -17,7 +17,7 @@ Read the Docs Sphinx Theme
   :alt: Documentation Status
 
 The ``sphinx_rtd_theme`` is a sphinx_ theme designed to look modern and be mobile-friendly.
-This theme is primary focused to be used on readthedocs.org_ but can work with your
+This theme is primarily focused to be used on readthedocs.org_ but can work with your
 own sphinx projects. To read more and see a working demo_ head over to readthedocs.org_.
 
 .. _sphinx: http://www.sphinx-doc.org