Allow to use env var to set hostname

Refs #39

README.md

@@ -53,6 +53,11 @@ If you don't have a domain/subdomain pointing to your server yet, you can use th
 docker run -d -p 80:80 -h <servers-external-ip-address> sverhoeven/cartodb
 ```
 
+Instead of setting hostname with `-h` you can also use the `CARTO_HOSTNAME` environment variable with:
+```
+docker run -d -p 80:80 -e CARTO_HOSTNAME=<servers-external-ip-address> cartodb.example.com sverhoeven/cartodb
+```
+
 Persistent data
 ---------------
 

startup.sh

@@ -1,6 +1,8 @@
 #!/bin/bash
 
-perl -pi -e 's/cartodb\.localhost/$ENV{"HOSTNAME"}/g' /etc/nginx/sites-enabled/default /cartodb/config/app_config.yml /Windshaft-cartodb/config/environments/development.js
+CARTO_HOSTNAME = ${CARTO_HOSTNAME:=$HOSTNAME}
+
+perl -pi -e 's/cartodb\.localhost/$ENV{"CARTO_HOSTNAME"}/g' /etc/nginx/sites-enabled/default /cartodb/config/app_config.yml /Windshaft-cartodb/config/environments/development.js
 
 service postgresql start
 service redis-server start