add introduction and build reqs to readme.txt

readme.txt

@@ -2,7 +2,7 @@ Quick Start
 -----------
 
 on Linux:
- $ export JAVA_HOME=/usr/local/java
+ $ export JAVA_HOME=/usr/local/java # or wherever you have Java installed
  $ make
  $ build/linux-i386-compile-fast/avian -cp build/test Hello
 
@@ -12,6 +12,25 @@ on Mac OS X:
  $ build/darwin-i386-compile-fast/avian -cp build/test Hello
 
 
+Introduction
+------------
+
+Avian is a lightweight virtual machine and class library designed to
+provide a useful subset of Java's features, suitable for building
+self-contained applications.  More information is available at the
+project web site:
+
+  http://oss.readytalk.com/avian
+
+If you have any trouble building, running, or embedding Avian, please
+post a message to our discussion group:
+
+  http://groups.google.com/group/avian
+
+That's also the place for any other questions, comments, or
+suggestions you might have.
+
+
 Supported Platforms
 -------------------
 
@@ -29,6 +48,18 @@ but patches to enable them are welcome.
 Building
 --------
 
+Build requirements include:
+
+  * GNU make 3.80 or later
+  * GCC 3.4 or later
+  * JDK 1.5 or later
+  * GNU binutils 2.17 or later (not needed on OS X)
+  * MinGW 3.4 or later (only if cross-compiling for Windows)
+  * zlib 1.2.3 or later
+
+Earlier versions of some of these packages may also work but have not
+been tested.
+
 The build is directed by a single makefile and may be influenced via
 certain flags described below.