doc review: be clear about using any language or Python with libraries

First, the wording was not clear about the language choices and the
added benefits of using Python. Also, let's focus on using the term
libraries instead of APIs. Libraries are an important part of Avocado
(see definition of what Avocado is) and IMHO denote more value than
the term APIs does.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

docs/source/Introduction.rst

@@ -12,8 +12,8 @@ executable can serve as a test.
 Avocado is composed by:
 
 * A test runner that lets you execute tests. Those tests can be either written in your
-  language of choice, or use the Python API available. In both cases, you get
-  facilities such as automated log and system information collection.
+  language of choice, or be written in Python and use the available libraries. In both
+  cases, you get facilities such as automated log and system information collection.
 
 * APIs that help you write tests in a concise, yet expressive way.
   The Test API is the whole set of modules, classes and functions available