Update README.md file

[chetan2309]

When I ran the code using the acquire(path_to_file) command first and then ran process command like this process(brightness); I got this error

Not enough input arguments.

Error in process (line 13)
[b, a] = butter(2, [(((BPM_L)/60)/fps*2) (((BPM_H)/60)/fps*2)]);

The code in the process.m doesn't have any provision to take default value for fps. So if you could update the README file.

Later I ran the command like this

process(brightness, 50);

P.S:- I have very limited understanding of MATLAB.