fix typo (#85)

Author: rcsanchez97

source/get-started/download-and-install.txt

@@ -16,7 +16,7 @@ Download and Install
 
    .. step:: Install dependencies
 
-      Before you being this tutorial, ensure you have the following dependencies
+      Before you begin this tutorial, ensure you have the following dependencies
       installed in your development environment:
 
       - Compiler that supports C++17, such as `GCC <https://gcc.gnu.org/install/>`__, `Clang <https://clang.llvm.org/>`__,