Added jar files access note to the knowledge base

knowledge base/access a jar file contents.md

@@ -0,0 +1,14 @@
+# Access a jar file's contents
+
+A `.jar` file is nothing more than an archive.  
+You can find all the files it contains just unzipping it:
+
+```shell
+$ unzip file.jar
+Archive:  file.jar
+   creating: META-INF/
+  inflating: META-INF/MANIFEST.MF
+   creating: org/
+  …
+  inflating: META-INF/maven/org.apache.hive/hive-contrib/pom.properties
+```