[cli] fix typo in joiner readme doc (#6009)

diff --git a/src/cli/README_JOINER.md b/src/cli/README_JOINER.md
index 6d8c2ab..715ccdb 100644
--- a/src/cli/README_JOINER.md
+++ b/src/cli/README_JOINER.md
@@ -18,7 +18,7 @@
 
 Usage: `joiner help`
 
-Print dataset help menu.
+Print joiner help menu.
 
 ```bash
 > joiner help