Add support for createInstance without descriptor

[bnason-nf]

diff --git a/include/webgpu.hpp b/include/webgpu.hpp
index d60066a..f98465b 100644
--- a/include/webgpu.hpp
+++ b/include/webgpu.hpp
@@ -1267,12 +1267,16 @@ END
 
 
 Instance createInstance(const InstanceDescriptor& descriptor);
+Instance createInstance();
 
 #ifdef WEBGPU_CPP_IMPLEMENTATION
 
 Instance createInstance(const InstanceDescriptor& descriptor) {
        return wgpuCreateInstance(&descriptor);
 }
+Instance createInstance() {
+       return wgpuCreateInstance(nullptr);
+}
 
 // Handles members implementation
 // Methods of ChainedStruct