docs: fix incorrect tmux configurations in README.md

[hangxingliu]

Awesome project! I just installed it and configured it by following your README document. I realized that there are some incorrect configurations that cannot work correctly and will cause errors in the README file.

An example error:

~/.tmux.conf:30:  Empty value

References:

• https://man7.org/linux/man-pages/man1/tmux.1.html#:~:text=are%20as%20follows%3A-,set%2Doption%20%5B,-%2DaFgopqsuUw%5D%20%5B%2Dt

[Sneethe]

TY!
This has been annoying me for ages until I worked out what was causing the error.