Removed preferredScheme in favor of baseUrl

As suggested in #102 and added documentation for baseUrl

Signed-off-by: Alan Cha <[email protected]>

Author: Alan-Cha

packages/oasgraph/README.md

@@ -79,6 +79,8 @@ The options object can contain the following properties:
 
 * `fillEmptyResponses` (type: `boolean`, default: `false`): OASGraph, by default, will only wrap operations that have a [response schema](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.0.md#responsesObject) and operations that do not have a response schema will be ignored. The reason is that all GraphQL objects must have a data structure and in these cases, where the OAS does not define a response schema, the data structure cannot be safely assumed. As a result, it is recommended that the OAS should be modified to include a response schema. However, under certain circumstances, some operations should _not in fact_ have a response schema. One circumstance is HTTP status code 204, in which no content should be returned. The option `fillEmptyResponses` will allow OASGraph to wrap these operations by assigning these operations a nullable data structure. Although this data structure is meaningless, the operation will appear in the schema. 
 
+* `baseUrl` (type: `string`): Used to manual specify the base URL which all paths will be built on. Normally, OASGraph will select a base URL from the [server object](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.2.md#serverObject) defined in the OAS. However, if the server object contains multiple URLs, OASGraph will randomly select one. The purpose of this option is to provide greater control over the base URL in these situations, especially when the OAS cannot be modified. This option may also prove to be useful in testing and development. 
+
 Consider this example of passing options:
 
 ```javascript