doc: fix warning indicator

Signed-off-by: Soc Virnyl Estela <contact@uncomfyhalomacro.pl>

README.md

@@ -148,7 +148,7 @@ the root folder of the project.
 A new option is added to respect lockfiles. This means that vendored tarballs
 are expected to have the same metadata inside the `Cargo.lock`.
 
-> ![WARNING] `cargo-vendor-filterer` is not supported for lockfile validation/verification
+> [!WARNING] `cargo-vendor-filterer` is not supported for lockfile validation/verification
 at this time.
 
 # How to do multiple vendors