improve README

Author: maxxbw

README.md

@@ -1,8 +1,23 @@
 # FixBench
 
-## Description
 A benchmark for example-based program transformation with bug-fixing code changes.
 
+* [All](https://github.com/Example-based-Program-Transformation/FixBench/tree/master/All): All code changes (i.e., complete benchmark).
+* [WithinSingleMethod](https://github.com/Example-based-Program-Transformation/FixBench/tree/master/WithinSingleMethod): All code changes within single method.
+
+## Example
+An Example Code Change for Fixing Null Pointer Dereference in **FixBench** [[Original GitHub](https://github.com/orientechnologies/orientdb/commit/529e81f4211096e6468a51d8bbd8968b60156762)]
+
+```diff
+diff --git a/core/src/main/java/com/orientechnologies/orient/core/db/document/ODatabaseDocumentTx.java b/core/src/main/java/com/orientechnologies/orient/core/db/document/ODatabaseDocumentTx.java
+index c9ff80d..8b733ad 100755
+--- a/core/src/main/java/com/orientechnologies/orient/core/db/document/ODatabaseDocumentTx.java
++++ b/core/src/main/java/com/orientechnologies/orient/core/db/document/ODatabaseDocumentTx.java
+@@ -251 +251 @@ public class ODatabaseDocumentTx extends OListenerManger<ODatabaseListener> impl
+-        if (!name.equals(iUserName)) {
++        if (name== null || !name.equals(iUserName)) {
+```
+
 ## Statistic
 | Id |  Bug Type | Bug Description | \# Code Changes |
 |:-----------:|:------------------------:|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|:------------------------:|
@@ -16,3 +31,4 @@ A benchmark for example-based program transformation with bug-fixing code change
 |       |                          |     Total                                                                                                                                                                          |           1,023          |
 
 
+