Request for updating README.MD

Before anything, I'd like to thank you for this amazing repo.

I just want to say it's good to mention this fact (in readme.md) that reloading a `systemd` service will not update service environment vars.

Having such a systemd unit file:
```
[Unit]
Description=Service using tableflip

[Service]
EnvironmentFile=/path/to/config-file
ExecStart=/path/to/binary -some-flag /path/to/pid-file
ExecReload=/bin/kill -HUP $MAINPID
PIDFile=/path/to/pid-file
```
By updating the config-file content and executing `systemctl reload service`, the reloaded service will not get new/updated environment vars. The service should read its configs/envs itself.