When performing valuation using P/E ratio, what is the importance of comparing it with the industry P/E ratio? Where can I find the industry P/E ratio without doing manual calculation?

The purpose of using financial ratios is for comparison between competitors of the same sector. Companies from different industries would have vastly different average P/E ratios.

Knowing the industry P/E allows you to gauge whether the company is potentially over or under-priced within the industry. You can look for the data at Bloomberg under marketssectors.