How to add temperature tab to task manager?

Try HardWare Monitor:

HWMonitor is a hardware monitoring program that reads PC systems main health sensors : voltages, temperatures, fans speed. The program handles the most common sensor chips, like ITE® IT87 series, most Winbond® ICs, and others. In addition, it can read modern CPUs on-die core thermal sensors, as well has hard drives temperature via S.M.A.R.T, and video card GPU temperature.

If you wish to see only the CPU temperature, and are not concerned about anything else, Core Temp is a more compact, smaller foot print program:

The uniqueness of it is that it shows the temperature of each individual core in each processor in your system! You can see in real time how the CPU temperature varies when you load your CPU. It's also completely motherboard independent.