Document how to use color option

[djmgit]

Please document how to use color option while plotting function under the ** Using PlotIt ** section. Also add an example showing how to use color option.

[Aniq55]

@LoneOne123 you may take this up as you've worked with color options.

[LoneOne123]

Will have a look at this later on the day

[LoneOne123]

Ok thats the text i would append to the description on using plot
Color defines color of the plot line and have to be in low case letters (as word) or in hexformat (in single quotes).

And that are the 2 examples i would append
python plotit.py -f 'sin(x)' -c green
python plotit.py -f 'sin(x)' -c '#008000'

If its ok i would commit it and create a pr, but please have a look on correctnes of spelling and grammar im not a native speaker so maybe there are some mistakes ;)
greets

[ankan17]

Since I see that documentation for color has not still been added, I'd like to do that @djmgit