Add better usage instructions to the README (#69)

* better usage instructions

* documentation info

---------

Co-authored-by: Yey007 <55263178+Yey007@users.noreply.github.com>

Author: utkudotdev

README.md

@@ -5,7 +5,6 @@
 ![Docs Badge](https://github.com/cornellev/icp/actions/workflows/docs.yaml/badge.svg)
 
 ## Introduction
-
 This repository hosts CEV's implementation of Iterative Closest Points (ICP) as applied to scan matching.
 
 ## Authors
@@ -19,12 +18,29 @@ Please see [LICENSE](LICENSE). Note that all code is licensed under the MIT lice
 ## Install
 You can view installation instructions at [INSTALL.md](INSTALL.md).
 
-## Usage and Documentation
-We host the usage information and documentation at [cornellev.github.io/icp/](https://cornellev.github.io/icp/).
-Please see there for information on how to download and how to use or extend the library.
-
-You can build the documentation yourself locally with `make docs`.
-The main page will be located at `docs/index.html` relative to the project root.
+## Usage
+```cpp
+#include "icp/icp.h"
+#include "icp/geo.h"
+#include "icp/driver.h"
+#include <iostream>
+
+void align_clouds(const icp::PointCloud2& a, const icp::PointCloud2& b) {
+    std::unique_ptr<icp::ICP2> icp = icp::ICP2::from_method("vanilla", icp::Config()).value();
+    icp::ICPDriver driver(std::move(icp));
+
+    driver.set_max_iterations(100);
+    driver.set_transform_tolerance(0.1 * M_PI / 180, 0.1);
+    auto result = driver.converge(a, b, icp::RBTransform2::Identity());
+
+    std::cout << "Rotation: " << result.transform.rotation() << "\n";
+    std::cout << "Translation: " << result.transform.translation() << "\n";
+}
+```
+
+## Documentation
+Some documentation is available in the `book` folder. There are also Doxygen docs and other generated documentation hosted at 
+[cornellev.github.io/icp/](https://cornellev.github.io/icp/), but we haven't update this system in a bit and it might be out of date.
 
 ## Versions
 Version information can be found in the [releases](https://github.com/cornellev/icp/releases) page.