📚 document allowed colors

[strazto]

I wanted to colourize by calendars, and noticed, from a screenshot, that there was a way to do so:

--calendar="calendar name#color"

Yay!

So I started adding these to my rc file, but hit an error on #purple.

I looked up this in the issues and found that someone described something about using google's colour names for calendars.

I thought that sounded reasonable, so I started to edit my colours to match googles, before getting an error for doing so.

I tried to search the man page, but there was no indication. I didn't really want to guess about what would or wouldn't work.

Finally, since I knew that this was being thrown by the arg parser, I checked the code in argparse, followed that through to printer and got the following:

gcalcli/gcalcli/printer.py

Lines 4 to 7 in aa287f9

	COLOR_NAMES = set(('default', 'black', 'red', 'green', 'yellow', 'blue',
	'magenta', 'cyan', 'white', 'brightblack', 'brightred',
	'brightgreen', 'brightyellow', 'brightblue',
	'brightmagenta', 'brightcyan', 'brightwhite'))

I recognize that these are the ANSII escape colours, which I might have guessed, but I didn't know.

I know it sounds petty, but I'm disappointed to have gone through so much work to colourize my outputs. I would really like this option to be documented in the argparse output, so the error is less ambiguous.