Update README.md: baseURL parameter

README.md

@@ -140,6 +140,7 @@ You can create a new instance of axios with a custom config.
 
 ```js
 var instance = axios.create({
+  baseURL: 'https://some-domain.com/api/',
   timeout: 1000,
   headers: {'X-Custom-Header': 'foobar'}
 });
@@ -165,6 +166,11 @@ These are the available config options for making requests. Only the `url` is re
 {
   // `url` is the server URL that will be used for the request
   url: '/user',
+  
+  // `baseURL` will be prepended to `url` unless `url` is absolute. 
+  // It can be convenient to set `baseURL` for an instance of axios to pass relative URLs 
+  // to methods of that instance.
+  baseURL: 'https://some-domain.com/api/',
 
   // `method` is the request method to be used when making the request
   method: 'get', // default