git-cola.rst: wrap long lines and make minor sentence adjustments

Signed-off-by: David Aguilar <davvid@gmail.com>
cmds: fix patch export when using Python3

reversed() is an iterator so expand the FormatPatch arguments
into lists so that we can index into them.

Closes #290

Reported-by: Ｖ字龍(Vdragon) <pika1021@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>