Add user doc for the macro

Author: VasanthakumarV

einops-macros/src/lib.rs

@@ -1,5 +1,12 @@
 mod einops;
 
+/// Macro to perform tensor transformations using simple expressions
+///
+/// # Example
+///
+/// ```no_run
+/// let output = einops!("h w c -> c h w", &input);
+/// ```
 #[proc_macro]
 pub fn einops(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     einops::einops(input.into())