Added Carton's local directory

[jonasbn]

I am a user of Carton. Carton is a dependency manager for Perl, much like Bundler for Ruby.

Carton creates a local directory with the dependency file tree named local/ just as for example: node_modules.

Carton installation documentation recommends adding this particular directory to: .gitignore, see: https://metacpan.org/pod/Carton#Initializing-the-environment

echo local/ >> .gitignore

Carton is widely used for Perl development and on the same level as the other tools listed in the Perl gitignore file.