Add README

README.md

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+# roto
+
+Rust protos without the P.
+
+The codegen is different; we don't create data structures.
+We mark what where each field is, and only read it when asked.
+The binary blob is never decompressed by the library; it is your
+job to figure out how to store the data if you need to access it
+more than once.
+
+And building protos? You use a builder. We don't make some fancy
+structure and give you a marshal function, nah. You give us a blob
+to write data into, and we write what you tell us, no questions asked.
+
+### Sample usage
+
+```rust
+/*
+message Hello {
+    string hello_world = 1;
+    message InnerWorld {
+        string thought = 1;
+    }
+    InnerWorld inner_world = 2;
+}
+ */
+
+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)?;
+    // Load the hello world string; returns bytes, not
+    // a Rust string.
+    let hello_world = accessor.hello_world()?;
+    // Inspect a nested message; accessing inner_world scans it
+    // for flag locations and returns a similiar access struct
+    let inner_world = accessor.inner_world()?.thought()?;
+
+    format!("{} is about {}", hello_world, inner_world)
+} 
+```
+
+### High level design
+
+The runtime library offers an iterator over the fields in a message, using the protobuf wire format provide
+objects of flag and type. Codegen creates a 'wrapper' that iterates over the message, and records the
+byte offset of each element. Helper methods in the wrapper give the user access to the name fields,
+casted to the appropriate data type.
+
+### Literature
+
+https://protobuf.dev/programming-guides/encoding/