Parameters for Get, Put, and Accumulate are not explained clearly

[robertodr]

I had some questions on the meaning and use of the target_disp parameter in the RMA functions. For the next iteration:

• Add figure(s) to explain how these functions compute the address on the target process using information known to the window object (disp_unit)
• Add example(s) (they could be exercises) that require more thinking as to what should be passed for these parameters.