lefthook add pre-commit

This command will try to build the following structure in repository:
├───.git
│   └───hooks
│       └───pre-commit // this executable will be added. Existing file with
│                      // same name will be renamed to pre-commit.old
(lefthook adds these dirs if you run the command with the -d option)
│
├───.lefthook          // directory for project level hooks
│   └───pre-commit     // directory with hook executables
└───.lefthook-local    // directory for personal hooks; add it in .gitignore
    └───pre-commit
