How to tell the user to click to edit data

I'm developing a website which basically contains all the info about a series of projects (a few hundreds). Each project has its dedicated page with all info about it (dates, classifications, schedule, budget, employees...). I wanted the data to be very easy to edit, so I used inline editing. You can click on any data to change it, and all the other values update themselves Excel style.

I've tested the prototype version on some of the future users, and each one of them asked me:

How do I edit the data?

None of them thought of clicking.

So my question is, how can make my users click on a text, date, number to edit it?