By Lars Mucklejohn Employees at computer firm Raspberry Pi are poised to enjoy an up to £68m windfall from the company’s float on the London stock market in the coming weeks. According to a London Stock Exchange filing, the Cambridge-based firm’s employee incentive scheme controls a roughly 13.6 per cent stake in Raspberry Pi. If the firm achieves the £500m IPO valuation it is reportedly seeking, the employee shares would be worth an average of up to £660,000 for each of its 103 staff members when converted into ordinary shares. The final figure will likely be diluted by Raspberry Pi issuing n…