Add Notes

"Notes.txt" file is general study notes with practical tips on Ruby
programming
Revert "Add Notes"

This reverts commit 57a476a312d4b16f2c2c2bfd7317b89855dd9010.
Revert "Revert "Add Notes""

This reverts commit c62603ec8f5ee50b1562e941db15a6a89779ea4f.