First pass at runtime

README.md

@@ -1,6 +1,6 @@
 # roto
 
-Rust protos without the P.
+Rust protos without the pointers.
 
 The codegen is different; we don't create data structures.
 We mark what where each field is, and only read it when asked.
@@ -28,7 +28,7 @@ message Hello {
 fn parse_proto(data: &[u8]) -> Result<String> {
     // Scans the data, marks where each flag is as an offset
     // into the proto.
-    let accessor = HelloProto::new(accessor)?;
+    let accessor = HelloProto::new(data)?;
     // Load the hello world string; returns bytes, not
     // a Rust string.
     let hello_world = accessor.hello_world()?;
@@ -40,6 +40,16 @@ fn parse_proto(data: &[u8]) -> Result<String> {
 } 
 ```
 
+### Sample builder usage
+
+```rust
+let mut buf = [0u8; 1024];
+let mut builder = ProtoBuilder::new(&mut buf);
+builder.write_string(1, "hello world")?;
+builder.write_int32(2, 42)?;
+let data = builder.finish()?; // returns the used slice of the buffer
+```
+
 ### High level design
 
 The runtime library offers an iterator over the fields in a message, using the protobuf wire format provide