fix --set-param ref (#2450)

content/docs/command-reference/exp/run.md

@@ -157,11 +157,11 @@ CPU cores).
 > In addition to the following, `dvc exp run` accepts all the options in
 > `dvc repro`, with the exception that `--no-commit` has no effect here.
 
-- `-S [<filename>:]<params_list>`, `--set-param [<filename>:]<params_list>` -
-  set the specified `dvc params` for this experiment. `filename` can be any
-  valid params file (`params.yaml` bu default). `params_list` accepts a
-  comma-separated list of key-value pairs in the form `key1=val1,key2=val2...`.
-  This will override the param values coming from the params file.
+- `-S [<filename>:]<param_name>=<param_value>`,
+  `--set-param [<filename>:]<param_name>=<param_value>` - set the specified
+  `dvc params` for this experiment. `filename` can be any valid params file
+  (`params.yaml` by default). This will override the param values coming from
+  the params file.
 
 - `-n <name>`, `--name <name>` - specify a name for this experiment. A default
   name will generated by default, such as `exp-f80g4` (based on the experiment's