Added 21 Lessons for the 21st Century

[MLpranav]

In this pull request

• [X] I am adding a new book.

Adding new book

• The book I am adding is 21 Lessons for the 21st Century.
• I am adding this book to Philosophy And Psychology section.
• I have read this book 2 times.
• I think this book deserves to be in this list because it examines the scientific and cultural changes that have transformed human societies across the world.

[MLpranav]

@hackerkid kindly accept the PR, else add a hacktoberfest-accepted label. Thanks.

[hackerkid]

I am going through all the old PRs in the repo. I might have closed this because of one of the following

• There is no description.
• The book is added in the wrong order.
• Have lot of merge conflicts

Sorry for closing the PR. But feel free to create a new one!