Add `--no-browser` Flag

[felixhummel]

First of all: Thanks for writing this! I like its simplicity.

Second, it would be nice to have the option not to open the browser when running sphinx-reload, e.g.

sphinx-reload --no-browser .

AFAICT this would mean adding the option to the parser, passing it to _run and setting open_url_delay=None if it is set.

Should I give it a shot?