docs(README.md): update link to installer script

Signed-off-by: Edouard Lopez <dev+git@edouard-lopez.com>
docs(README.md): rename 'proxy' to 'proxy-ssh'

Signed-off-by: Edouard Lopez <dev+git@edouard-lopez.com>
feat(proxy-ssh): add 'reload', 'force-reload' and 'graceful' subcommand

Just the interfaces, not really implement as I'm not
aware a config file to 'reload'.

Signed-off-by: Edouard Lopez <dev+git@edouard-lopez.com>
fix(proxy-ssh,status): get the pid of the Python command

To know if the service is up, I need to check if sshuttle is up.
Sshuttle is a python script. 'proxy-ssh' has no existence as a process.

Signed-off-by: Edouard Lopez <dev+git@edouard-lopez.com>