docs: add usage

Signed-off-by: msclock <[email protected]>

Author: msclock

README.md

@@ -1,3 +1,34 @@
 # A cmake registry
 
 This is a cmake modules registry based on vcpkg and accepts cmake module registration.
+
+## Usage
+
+Just register the cmake registry to the vcpkg configuration.
+
+```json
+{
+  "registries": [
+    {
+      "kind": "git",
+      "baseline": "8c971ad168027d4c3acbd2b3a2752b80e0859fef",
+      "repository": "https://github.com/msclock/cmake-registry",
+      "packages": [
+        "cmake-modules",
+        "vcpkg-cmake-module"
+      ]
+    }
+  ]
+}
+```
+Add the modules to vcpkg dependencies.
+
+```json
+{
+  "dependencies": [
+    "cmake-modules"
+  ]
+}
+```
+
+There is a real [example](https://github.com/msclock/cpp-scaffold) can refer.