add documentation fragment to header file

src/unpack.hh

@@ -62,6 +62,29 @@ namespace SignedPackage {
             std::filesystem::path target_path
         );
 
+/*  how to provision for a user and use this API
+
+    #include <pEp/unpack.hh>
+
+    void provision(std::string url)
+    {
+        pEp::UpdateClient::product p { "provisioning data", url };
+
+        UpdateClient::PublicKey update_key;
+        UpdateClient::load_key("update_key.der");
+
+        CryptoPP::ed25519PublicKey deployment_key;
+        SignedPackage::LoadPublicKey("deployment_key-pub.der", deployment_key);
+
+        CryptoPP::RSA::PrivateKey provisioning_key;
+        SignedPackage::LoadPrivateKey("provisioning_key.der", provisioning_key);
+
+        SignedPackage::provision_user(p, update_key, deployment_key,
+                provisioning_key);
+    }
+
+*/
+
     void provision_user(
             pEp::UpdateClient::product p,
             pEp::UpdateClient::PublicKey update_key,