LONDON (Reuters) – Pippa Middleton, the sister of the Duchess of Cambridge, is to give cooking tips to the masses in a new column for British supermarket chain Waitrose. Middleton, 29, will write a column for the upmarket chain’s monthly magazine, Waitrose Kitchen, called “Pippa’s Friday Night Feasts”. Her foray into kitchen advice comes after she released a book called “Celebrate” last year, which was a guide to entertaining through the year and built on the experience she gained working for her family’s party-planning business. …