add a standalone readme file for milestone 2

Author: wsw-stack

README-M2.md

@@ -0,0 +1,16 @@
+# Milestone 2
+
+For the Milestone 2 of SWE262P, 2 new functions were added:
+
+```java
+static JSONObject toJSONObject(Reader reader, JSONPointer path) 
+static JSONObject toJSONObject(Reader reader, JSONPointer path, JSONObject replacement) 
+```
+
+The first one takes in 2 parameters, a `Reader` object which contains some XML input and a `JSONPointer` object that includes a json path for querying, and returns a `JSONObject` object which has the corresponding path, or throw an error if that path does not exist.
+
+The first one takes in 3 parameters, a `Reader` object which contains some XML input and a `JSONPointer` object that includes a json path for querying, and a `JSONObject` for replacement. And returns a new `JSONObject` object which has the corresponding path replaced with the new given object, or throw an error if that path does not exist.
+
+Both new functions are placed in the `XML.java` file.
+
+The test cases of the functions are placed under the `org.json.junit.milestone2.tests` package, and to run the test case which deals with large file input, first create a folder named `xml_files` under the `/src/test/resources` path, and put the xml files for testing under this path.