update readme with note about v0.5.x compatibility

Author: brianc

README.md

@@ -5,6 +5,9 @@ Non-blocking PostgreSQL client for node.js.  Pure JavaScript and native libpq bi
 ## Installation
 
     npm install pg
+    
+### notice
+node-postgres compiles native bindings when you install.  The native bindings do not _currently_ compile with node v0.5.x.  I'm working on support for v0.5.x.  In the mean time if you get a compilation failure during installation you have still successfully installed the module; however, you cannot use the native bindings -- only the pure javascript bindings.
 
 ## Examples