CLI: add example as documentation epilogue

Write examples in cli's epilgue like in csvspoon:

Examples: Operate NATURAL JOIN on two csv files: csvspoon join file1.csv file2.csv

Operate two NATURAL JOIN on three csv files: csvspoon join file1.csv file2.csv file3.csv

Operate LEFT JOIN on two csv files csvspoon join -l file1.csv file2.csv

Operate RIGHT JOIN on two csv files csvspoon join -r file1.csv file2.csv

Operate OUTER JOIN on two csv files csvspoon join -lr file1.csv file2.csv