add tags to books to categorise them

[sharovatov]

the draft of the list:

• Personal development for books which aren't that much related to anything in engineering in particular
• Engineering — any engineering
• Software engineering — just the software engineering, smth like Kent Beck books
• Leadership — Deming / Ackoff ??
• Web development
• Engineering management — similar to leadership?
• Game development
• Software testing
• Quality assurance

[sharovatov]

CamelCase them, obviously