Add CMakePresets and update README instructions

Using a `CMakePresets.json` file makes it much easier to manage
several alternate build configurations, such as the "ClangCL"
build for Windows. This also makes it easier for tools like
VSCode to run CMake-based builds.

CMakePresets.json

@@ -0,0 +1,59 @@
+{
+    "version": 3,
+    "cmakeMinimumRequired": {
+      "major": 3,
+      "minor": 11,
+      "patch": 0
+    },
+    "configurePresets": [
+      {
+        "name": "__defaults__",
+        "hidden": true,
+        "binaryDir": "${sourceDir}/build"
+      },
+      {
+        "name": "make",
+        "inherits": "__defaults__",
+        "displayName": "Make",
+        "description": "Unix Makefiles",
+        "generator": "Unix Makefiles",
+        "binaryDir": "${sourceDir}/build"
+      },
+      {
+        "name": "windows",
+        "inherits": "__defaults__",
+        "displayName": "Windows",
+        "description": "Visual Studio 2022 with Clang/LLVM frontend",
+        "generator": "Visual Studio 17 2022",
+        "toolset": "ClangCL",
+        "condition": {
+          "type": "equals",
+          "lhs": "${hostSystemName}",
+          "rhs": "Windows"
+        }
+      }
+    ],
+    "buildPresets": [
+      {
+        "name": "__defaults__",
+        "hidden": true,
+        "targets": [
+            "gemma",
+            "libgemma"
+        ]
+      },
+      {
+        "name": "make",
+        "inherits": "__defaults__",
+        "displayName": "Unix Makefiles",
+        "configurePreset": "make"
+      },
+      {
+        "name": "windows",
+        "inherits": "__defaults__",
+        "displayName": "Windows",
+        "configuration": "Release",
+        "configurePreset": "windows"
+      }
+    ]
+  }

README.md

@@ -55,6 +55,16 @@ Before starting, you should have installed:
   least C++17.
 - `tar` for extracting archives from Kaggle.
 
+Building natively on Windows requires the Visual Studio 2012 Build Tools with the
+optional Clang/LLVM C++ frontend (`clang-cl`). This can be installed from the
+command line with
+[`winget`](https://learn.microsoft.com/en-us/windows/package-manager/winget/):
+
+```sh
+winget install --id Kitware.CMake
+winget install --id Microsoft.VisualStudio.2022.BuildTools --force --override "--passive --wait --add Microsoft.VisualStudio.Workload.VCTools;installRecommended --add Microsoft.VisualStudio.Component.VC.Llvm.Clang --add Microsoft.VisualStudio.Component.VC.Llvm.ClangToolset"
+```
+
 ### Step 1: Obtain model weights and tokenizer from Kaggle
 
 Visit [the Gemma model page on
@@ -104,25 +114,36 @@ The build system uses [CMake](https://cmake.org/). To build the gemma inference
 runtime, create a build directory and generate the build files using `cmake`
 from the top-level project directory:
 
-```sh
-cmake -B build
-```
-
-Then run `make` to build the `./gemma` executable:
+#### Unix-like Platforms
 
 ```sh
-cd build
-make -j [number of parallel threads to use] gemma
+# Configure `build` directory
+cmake --preset make
+
+# Build project using make
+cmake --build --preset make -j [number of parallel threads to use]
 ```
 
-For example, `make -j4 gemma` will build using 4 threads. If this is successful,
-you should now have a `gemma` executable in the `build/` directory. If the
-`nproc` command is available, you can use `make -j$(nproc) gemma`.
+If the `nproc` command is available, you can use `-j $(nproc)`.
+
+If this is successful, you should now have a `gemma` executable in the `build/` directory.
 
 > [!NOTE]
 > On Windows Subsystem for Linux (WSL) users should set the number of
 > parallel threads to 1. Using a larger number may result in errors.
 
+#### Windows
+
+```sh
+# Configure `build` directory
+cmake --preset windows
+
+# Build project using Visual Studio Build Tools
+cmake --build --preset windows -j [number of parallel threads to use]
+```
+
+If this is successful, you should now have a `gemma.exe` executable in the `build/` directory.
+
 ### Step 4: Run
 
 You can now run `gemma` from inside the `build/` directory.