Update test environment instructions

Tiny update to the documentation based on what I found trying to
get the test environment working. Simply need the Module::CAPIMaker
module installed via cpanm

README.md

@@ -39,6 +39,7 @@ The test environment variables have been set to use this install
 vagrant up
 vagrant ssh
 cd /vagrant
+cpanm Module::CAPIMaker
 make distclean; perl Makefile.PL; make
 
 #run all tests with test debugging