[nostalgia/developer-handbook] Update notes on error handling

deps/nostalgia/developer-handbook.md

@@ -227,6 +227,14 @@ int caller5(int i) {
 int caller6(int i) {
     return foo(i).unwrapThrow(); // unwrap will throw if there is an error
 }
+
+int caller7(int i) {
+    return foo(i).or_value(0); // will return 0 if foo returned an error
+}
+
+ox::Result<uint64_t> caller8(int i) {
+    return foo(i).to<uint64_t>(); // will convert the result of foo to uint64_t
+}
 ```
 
 Lastly, there are a few macros available to help in passing ```ox::Error```s