OLMIS-6558 Update README with description of the new env variable - P… (

#17)

* OLMIS-6558 Update README with description of the new env variable - PUBLIC_URL

* OLMIS-6558 Add information about optionality of PUBLIC_URL.

README.md

@@ -236,8 +236,9 @@ To see how to set environment variables through Docker Compose, see the
 
 The following environment variables are common to our services. They can be set either directly in compose files for images or provided as an environment file. See [docker-compose.yml](https://raw.githubusercontent.com/OpenLMIS/openlmis-ref-distro/master/docker-compose.yml) in the reference distribution for example usage. Also take a look at the sample [.env file](https://raw.githubusercontent.com/OpenLMIS/openlmis-config/master/.env) we provide. 
 
-* **BASE_URL** - The base url of the OpenLMIS distribution. Will be used in generated links pointing to this distribution, as well as for communication between services. Each service should communicate with others using BASE_URL as the base in order to avoid direct communication, which might not work in more complex deployments. Services should also use this variable if they wish to generate a link to the application. This should be an url, for example: https://example.openlmis.org
+* **BASE_URL** - The base url of the OpenLMIS distribution. Will be used for communication between services. Each service should communicate with others using BASE_URL as the base in order to avoid direct communication, which might not work in more complex deployments. If the PUBLIC_URL variable is not set, this variable will be used for the generated links. This should be an url, for example: https://example.openlmis.org
 * **VIRTUAL_HOST** - This is used by the nginx server as the virtual host under which the services are made avialble. This should be a host, for example: example.openlmis.org
+* **PUBLIC_URL** - The public url of the OpenLMIS distribution. Will be used in generated links pointing to this distribution. If this variable is not set, the BASE_URL will be used for the generated links. We extract this usage of BASE_URL to another environmental variable because in more complex deployments the BASE_URL does not have to be the base domain name. This should be an url, for example: https://example.openlmis.org
 * **CONSUL_HOST** - Identifies the IP address or DNS name of the Consul server. Set this to the host or IP under which the distribution is available and Consul listens for connections. Services should register with Consul under this address. This should be a host or an IP, for example 8.8.8.8.
 * **CONSUL_PORT** - The port used by the Consul server - services should use this port to register with Consul. This should be a port number, for example 8500. 8500 is used by default.
 * **REQUIRE_SSL** - Whether HTTPS is required. If set to `true`, nginx will redirect all incoming HTTP connections to HTTPS. By default SSL will not be required - either leave it blank or set to `false` if you wish to allow HTTP connections.