Adds configuration docs

Author: grussorusso

README.md

@@ -115,7 +115,7 @@ server:
 
 	$ bin/serverledge <config file>
 
-Supported configuration keys are defined in `internal/config/keys.go`.
+Further information about supported configuration options is available [here](./docs/configuration.md).
 
 ### Example
 

docs/configuration.md

@@ -0,0 +1,48 @@
+# Configuration #
+
+This page provides a (partial) list of configuration options that can
+be specified in Serverledge configuration files.
+All the supported configuration keys are defined in `internal/config/keys.go`.
+
+## Configuration files
+
+You can provide a configuration file using YAML or TOML syntax. Depending on the
+chosen format, the default file name will be `serverledge-conf.yaml` or
+`serverledge-conf.toml`. The file can be either placed in `/etc/serverledge`,
+in the user `$HOME` directory, or in the working directory where the server is
+started.
+
+Alternatively, you can indicate a specific configuration file when starting the
+server:
+
+	$ bin/serverledge <config file>
+
+
+## Frequently used options
+
+| Configuration key  | Description   | Example value(s) |
+| -------------      | ------------- | -----------------|
+| `etcd.address` | Hostname and port of the Etcd server acting as the Global Registry. | `127.0.0.1:2379` | 
+| `api.port` |Port number for the API server. | 1323| 
+| `cloud.server.url` |URL prefix for the remote Cloud node API. | `http://127.0.0.1:1326` | 
+| `factory.images.refresh` |Forces function runtime container images to be pulled from the Internet the first time they are used (to update them), even if they are available on the host.| `true` | 
+| `container.pool.memory` |Maximum amount of memory (in MB) that the container pool can use (must be not greater than the total memory available in the host).|4096| 
+| `janitor.interval` |Activation interval (in seconds) for the janitor thread that checks for expired containers.| 60| 
+| `container.expiration` |Expiration time (in seconds) for idle containers. | 600|
+| `registry.area` |Geographic area where this node is located.| `ROME`| 
+| `registry.udp.port` |UPD port used for peer-to-peer Edge monitoring.|| 
+| `scheduler.policy` |Scheduling policy to use. Possible values: `default`, `localonly`, `edgeonly`, `cloudonly`.|| 
+
+<!-- TODO:
+| `container.pool.cpus` ||| 
+| `cache.size` ||| 
+| `cache.cleanup` ||| 
+| `cache.expiration` ||| 
+| `scheduler.queue.capacity` ||| 
+| `metrics.enabled` ||| 
+| `metrics.prometheus.host` ||| 
+| `metrics.prometheus.port` ||| 
+| `registry.nearby.interval` ||| 
+| `registry.monitoring.interval` |||
+| `registry.ttl` ||| 
+-->