Improve documentation about environment variables being used (#138)

* add environment variables doc

* add link to env docs in README

* update as per review comments

* update docs

* update Readme

* update as per review comments

.gitignore

@@ -1 +1 @@
-bin/
+bin/

README.md

@@ -73,6 +73,8 @@ If you want to use your custom plugins as out-of-tree plugins in the simulator,
 
 ## Getting started
 
+Read more about environment variables being used in simulator server
+[here.](./simulator/docs/env-variables.md)
 ### Run simulator with Docker
 
 We have [docker-compose.yml](docker-compose.yml) to run the simulator easily.

simulator/docs/env-variables.md

@@ -0,0 +1,49 @@
+# Different Environment Variables used
+
+This page describes about the different environment variables that are
+used to configure kube-scheduler-simulator. 
+
+Please refer [docker-compose.yml](./../../docker-compose.yml) as an example
+use.
+
+`PORT`: (required) This is the port number on which kube-scheduler-simulator
+server is started.
+
+`KUBE_SCHEDULER_SIMULATOR_ETCD_URL`: (required) This is the URL for
+etcd. The simulator runs kube-apiserver internally, and the
+kube-apiserver uses this etcd.
+
+`CORS_ALLOWED_ORIGIN_LIST`: This URL represents the URL once web UI is
+started. The simulator and internal kube-apiserver set the allowed
+origin for `CORS_ALLOWED_ORIGIN_LIST`.
+
+`KUBECONFIG`: This is for the beta feature "Existing cluster
+Importing". This variable is used to find Kubeconfig required to
+access your cluster for importing resources to scheduler simulator.
+
+`KUBE_API_HOST`: This is the host of kube-apiserver which the
+simulator starts internally. Its default value is `127.0.0.1`.
+
+`KUBE_API_PORT`: This is the port of kube-apiserver. Its default
+value is `3131`.
+
+`KUBE_SCHEDULER_CONFIG_PATH`: The path to a KubeSchedulerConfiguration
+file.  If passed, the simulator will start the scheduler with that
+configuration.  Or, if you use web UI, you can change the
+configuration from the web UI as well.
+
+`ExternalImportEnabled`: This variable indicates whether the simulator
+will import resources from an existing cluster or not. Note, this is
+still a beta feature.
+
+## For Web UI
+
+`KUBE_API_SERVER_URL`: This is the kube-apiserver URL. Its default
+value is `http://localhost:3131`.
+
+`BASE_URL`: This is the URL for the kube-scheduler-simulator
+server. Its default value is `http://localhost:1212`.
+
+`ALPHA_TABLE_VIEWS`: This variable enables the alpha feature `table
+view`. Its value is either 0(default) or 1 (0 meaning disalbed, 1
+meaning enabled). We can see the resource status in the table.