Link beginner instructions in README.md

When navigating through the existing links in the README, it is not
immediately obvious where to go to find instructions in building
and testing the source code. Since the README is often the first
thing people see when looking at a repository, this information
should be front and centre so that newcomers to the project can
get setup as quickly as possible.

README.md

@@ -33,6 +33,11 @@ https://mariadb.com/kb/en/mariadb-versus-mysql-compatibility/
 
 https://mariadb.com/kb/en/new-and-old-releases/
 
+Getting the code, building it and testing it
+---------------------------------------------------------------
+
+Refer to the following guide: https://mariadb.org/get-involved/getting-started-for-developers/get-code-build-test/ which outlines how to correctly build the source code and run the MariaDB testing framework.
+
 Help
 -----