doc: fix minor grammatical errors (#489)

A missing "and" after "an" (which I do all the time) and some tense clarification.

src/lib.rs

@@ -71,8 +71,8 @@
 //! implement your own.
 //!
 //! Each widget follows a builder pattern API providing a default configuration along with methods
-//! to customize them. The widget is then rendered using the [`Frame::render_widget`] which take
-//! your widget instance an area to draw to.
+//! to customize them. The widget is then rendered using [`Frame::render_widget`] which takes
+//! your widget instance and an area to draw to.
 //!
 //! The following example renders a block of the size of the terminal:
 //!