fix incorrect command in helm dependency doc

helm add repo -> helm repo add

Signed-off-by: gangseok.lee <gangseok.lee@samsung.com>

docs/helm/helm_dependency.md

@@ -49,7 +49,7 @@ the dependency charts stored locally. The path should start with a prefix of
       repository: "file://../dependency_chart/nginx"
 
 If the dependency chart is retrieved locally, it is not required to have the
-repository added to helm by "helm add repo". Version matching is also supported
+repository added to helm by "helm repo add". Version matching is also supported
 for this case.