Add details about differences between js and native bindings (#1096)

README.md

@@ -139,7 +139,17 @@ var Pool = pg.Pool // good! a pool bound to the native client
 var Client = pg.Client // good! this client uses libpq bindings
 ```
 
-node-postgres abstracts over the pg-native module to provide exactly the same interface as the pure JavaScript version. Care has been taken to keep the number of api differences between the two modules to a minimum; however, it is recommended you use either the pure JavaScript or native bindings in both development and production and don't mix & match them in the same process - it can get confusing!
+#### API differences
+
+node-postgres abstracts over the pg-native module to provide the same interface as the pure JavaScript version. Care has been taken to keep the number of api differences between the two modules to a minimum.  
+However, currently some differences remain, especially :
+* the error object in pg-native is different : notably, the information about the postgres error code is not present in field `code` but in the field `sqlState` , and the name of a few other fields is different (see https://github.com/brianc/node-postgres/issues/938, https://github.com/brianc/node-postgres/issues/972).
+So for example, if you rely on error.code in your application, your will have to adapt your code to work with native bindings.
+* the notification object has a few less properties  (see https://github.com/brianc/node-postgres/issues/1045)
+* column objects have less properties (see https://github.com/brianc/node-postgres/issues/988)
+* the modules https://github.com/brianc/node-pg-copy-streams and https://github.com/brianc/node-pg-query-stream do not work with native bindings (you will have to require 'pg' to use them).
+
+Thus, it is recommended you use either the pure JavaScript or native bindings in both development and production and don't mix & match them in the same process - it can get confusing!
 
 ## Features