Small update to README

Adds the new script’s name.
Made core functions

-instead of build_all_libs (and a previously planned build_lib), I
prepared some variables and made it so that only one function
(build_libs) would do the stuff
-check_args function implementation (WIP)
-NO arguments == build all libs; ONE OR MORE == interpreted by a
function to “understand” what to do
-more string variables (including a conclusion variable, for when the
script finishes (partially-)successfully

-better variable placement