Update README

README.md

@@ -17,4 +17,54 @@ But *Simple-HL7v2* is a 18K .jar with a dependency only on Commons-Lang3, and if
 have a clear idea of the type of messages you'll be receiving and sending, and handle
 your own file or network transport, it may be all you need.
 
+# Download
 
+Download JARs and source from the GitHub [releases](https://github.com/jessepav/simple-hl7v2/releases)
+page.
+
+You'll need [Apache Commons Lang 3](http://commons.apache.org/proper/commons-lang/) in your
+classpath to use the library. An older version (3.4, compatible with Java 7) is in the `lib`
+directory of the source tree.
+
+# Usage
+
+For example code, see [examples/SimpleHL7v2Examples.java](https://github.com/jessepav/simple-hl7v2/blob/master/examples/SimpleHL7v2Examples.java)
+but basic usage is quite easy:
+
+```java
+HL7Parser parser = new HL7Parser();
+Message m = parser.parse(hl7text);
+
+String type = m.getMessageType();  // ex. "MDM^T02"
+
+String observationTimestamp1 = m.getField("OBR.7");  // Get a field value
+String observationTimestamp2 = m.getField("OBR(2).7");  // Get a field value from a repeated segment
+
+m.setField("OBR(1).8", observationTimestamp2);  // Change a field value
+
+HL7Encoder encoder = new HL7Encoder();
+String updatedHL7text = encoder.encode(m);
+
+```
+
+Programmatic construction of segment values is made more efficient by static helper
+methods like `indexed()` and `composite()`:
+
+```java
+Segment PID = new Segment("PID");
+PID.addFieldValue(2,
+	indexed(
+		1, "0493575",
+		4, composite("Big", null, "Elephant"),
+		5, "ID 1")
+);
+PID.addFieldValue(3, "454721");
+PID.addFieldValue(5, composite("DOE", "JOHN"));
+
+Message m = new Message();
+m.putSegment(PID);
+```
+
+# Javadoc
+
+Javadocs are available at [https://jessepav.github.io/simple-hl7v2/javadoc/](https://jessepav.github.io/simple-hl7v2/javadoc/).