add xml parsing part to README

Author: lindahua

README.md

@@ -1,5 +1,4 @@
-LightXML.jl
-============
+## LightXML.jl
 
 This package is a light-weight Julia wrapper of [Libxml2](http://www.xmlsoft.org), which provides a minimal interface that covers functionalities that are commonly needed:
 
@@ -8,3 +7,103 @@ This package is a light-weight Julia wrapper of [Libxml2](http://www.xmlsoft.org
 * Create an XML tree 
 * Export an XML tree to a string or an XML file
 
+### Setup
+
+Like other Julia packages, you may checkout *LightXML* from METADATA repo, as
+
+```julia
+Pkg.add("LightXML")
+```
+
+**Node:** This package relies on the library *libxml2* to work, which is shipped with Mac OS X and many Linux systems. So this package may work out of the box. If not, you may check whether *libxml2* has been in your system and whether *libxml2.so* (for Linux) or *libxml2.dylib* (for Mac) is on your library search path.
+
+### Examples
+
+The following examples show how you may use this package to accomplish common tasks.
+
+##### Read an XML file
+
+Suppose you have an XML file ``ex1.xml`` as below
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<bookstore>
+  <book category="COOKING" tag="first">
+    <title lang="en">Everyday Italian</title>
+    <author>Giada De Laurentiis</author>
+    <year>2005</year>
+    <price>30.00</price>
+  </book>
+  <book category="CHILDREN">
+    <title lang="en">Harry Potter</title>
+    <author>J K. Rowling</author>
+    <year>2005</year>
+    <price>29.99</price>
+  </book>
+</bookstore>
+```
+
+Here is the code to parse this file:
+
+```julia
+using MiniXML
+
+# parse ex1.xml:
+# xdoc is an instance of XMLDocument, which maintains a tree structure  
+xdoc = parse_file("ex1.xml")
+
+# get the root element
+xroot = root(xdoc)   # an instance of XMLElement
+# print its name
+println(name(xroot))  # this should print: bookstore
+
+# traverse all its child nodes and print element names
+for c in child_nodes(xroot)  # c is an instance of XMLNode
+    println(nodetype(c))
+    if is_elementnode(c)
+        e = XMLElement(c)  # this makes an XMLElement instance
+        println(name(e))
+    end
+end
+```
+
+There are actually five child nodes under ``<bookstore>``: the 1st, 3rd, 5th children are text nodes (any space between node elements are captured by text nodes), while the 2nd and 4th nodes are element nodes corresponding to the ``<book>`` elements. 
+
+One may use the function ``nodetype`` to determine the type of a node, which returns an integer following the table [here](http://www.w3schools.com/dom/dom_nodetype.asp). In particular, 1 indicates element node and 3 indicates text node.
+
+If you only care about child elements, you may use ``child_elements`` instead of ``child_nodes``. 
+
+```julia
+ces = collect(child_elements(xroot))  # get a list of all child elements
+@assert length(ces) == 2 
+
+# if you know the child element tagname, you can instead get a list as
+ces = get_elements_by_tagname(xroot, "book")
+
+e1 = ces[1]  # the first book element
+
+# print the value of an attribute
+println(attribute(e1, "category"))
+
+# find the first title element under e1
+t = find_element(e1, "title")
+
+# retrieve the value of lang attribute of t
+a = attribute(t, "lang")   # a <- "en"
+
+# retrieve the text content of t
+r = content(t)  # r <- "Everyday Italian"
+```
+
+One can also traverse all attributes of an element ``e`` as
+
+```julia
+for a in attributes(e)  # a is an instance of 
+	n = name(a)
+	v = value(a)
+	println("$n = $v")
+end
+```
+
+**Node:** The functions ``child_nodes``, ``child_elements``, and ``attributes`` return light weight iterators -- so that one can use them with for-loop. To get an array of all items, one may use the ``collect`` function provided by Julia.
+