🎉 完成

README.md

@@ -1,2 +1,12 @@
 # imgsz
 Image size analyzer for jpg/png/gif/webp
+
+# Usage
+
+```go
+// DecodeSize decodes the dimensions of an image that has
+// been encoded in a registered format. The string returned is the format name
+// used during format registration. Format registration is typically done by
+// an init function in the codec-specific package.
+func DecodeSize(r io.Reader) (Size, string, error)
+```