doc: Add no_std section

README.md

@@ -630,4 +630,9 @@ If `func3` does not handle the errors from `func1` and `func2`, it must return a
 `error_set` allows you to define errors quickly and precisely. Correctly scoping errors is easy and no wrapping of
 various error enum types is necessary. Conversions/Propagation up the stack are as simple as `.into()` or `?` (or `coerce!` macro).
 `error_set` also makes display messages and tracking context easy.
-By using `error_set`, your project can maintain clear and precise error definitions, enhancing code readability and maintainability without the tedious process of manually defining and managing error relations.
+By using `error_set`, your project can maintain clear and precise error definitions, enhancing code readability and maintainability without the tedious process of manually defining and managing error relations.
+
+### no_std
+
+This crate supports `#![no_std]`. All code generated from `error_set!` supports  `#![no_std]` except if using custom `#![display(...)]`
+messages.