Add installation and usage details to README

Author: axeal

README.md

@@ -4,4 +4,47 @@
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-A SolusVM Admin API Wrapper
+A SolusVM Admin API Wrapper
+
+## Installation 
+This module can be install via npm:
+```text
+$ npm install --save solusvm```
+
+## Usage
+
+The ```solusvm.call()``` method accepts three arguments:
+1. The name of the SolusVM API action to call
+2. An object with the variables for the API call
+3. An optional callback function
+
+If no callback function is passed to the call then a promise is returned. To use a callback instead, pass a callback function as the third argument.
+
+```javascript
+var solusvm = require('solusvm');
+
+//Configrure the API client with the URL, API ID and API KEY of the SolusVM Master Instance
+solusvm.configure('url', 'apiId', 'apiKey');
+
+//Example of a promise-based call to the client
+solusvm.call('node-idlist', {
+    type: 'openvz'
+  })
+  .then(function(data) {
+    console.log(data);
+  })
+  .catch(function(err) {
+    console.log(err);
+  });
+
+//Example of a callback-based call to the client
+solusvm.call('node-idlist', {
+    type: 'openvz'
+  }, function(err, data) {
+    if (err) {
+      console.log(err);
+    } else {
+      console.log(data);
+    }
+  });
+ ````