chore: README.md

README.md

@@ -140,3 +140,4 @@ spellbook my-spell target=127.0.0.1
 
 ## Known issues
 - `KEY=VAL my-cmd` inline environment variable syntax is currently not supported (will fail with `executable file not found in $PATH`)
+- Shell operators (such as `|`, `>>`, etc.) are not yet supported