Document the getConfig()-method in the plugin's restApi interface

Change-Id: I337456f3e83862b07469c581575e9912c29054fe

Documentation/pg-plugin-rest-api.txt

diff --git a/Documentation/pg-plugin-rest-api.txt b/Documentation/pg-plugin-rest-api.txt
index 70487ef..0d42bf6 100644
--- a/Documentation/pg-plugin-rest-api.txt
+++ b/Documentation/pg-plugin-rest-api.txt
@@ -25,6 +25,17 @@
 .Returns
 - Promise<string>
 
+== getConfig
+`repoApi.getConfig()`
+
+Get server config.
+
+.Params
+- None
+
+.Returns
+- Promise<Object>
+
 == get
 `repoApi.get(url)`