Mention that the host may also be changed with ENV variables

Was moving server, and re-installing crontab-ui. I need to access it from another pi in my home network, and stumbled upon how to set the host. Thought it was be good to mention in the main README.md.

Thanks for the awesome software by the way!

README.md

@@ -27,9 +27,9 @@ Get latest `node` from [here](https://nodejs.org/en/download/current/). Then,
     npm install -g crontab-ui
     crontab-ui
 
-If you need to set/use an alternate port, you may do so by setting an environment variable before starting the process:
+If you need to set/use an alternate host, or you need to set/use an alternate port, you may do so by setting an environment variable before starting the process:
 
-    PORT=9000 crontab-ui
+    HOST=0.0.0.0 PORT=9000 crontab-ui
     
 Also, you may have to **set permissions** for your `node_modules` folder. Refer [this](https://docs.npmjs.com/getting-started/fixing-npm-permissions).