Add prod build instructions

README.md

@@ -18,3 +18,8 @@ Then you can run the program with
 crystal run src/gtktest.cr
 ```
 
+You can build for production with
+
+```
+shards build -Dpreview_mt --release --no-debug
+```

shard.yml

@@ -5,7 +5,7 @@ authors:
   - Zoe Moore <zoenb@mailbox.org>
 
 targets:
-  gtktest:
+  wince:
     main: src/wince.cr
 
 dependencies: