Fix subcommands descriptions (#3977)

performance/shared/src/main/kotlin/org/jetbrains/benchmarksLauncher/launcher.kt

@@ -133,7 +133,7 @@ class BaseBenchmarkArguments(argParser: ArgParser): BenchmarkArguments(argParser
 
 object BenchmarksRunner {
     fun parse(args: Array<String>, benchmarksListAction: ()->Unit): BenchmarkArguments? {
-        class List: Subcommand("list") {
+        class List: Subcommand("list", "Show list of benchmarks") {
             override fun execute() {
                 benchmarksListAction()
             }

tools/benchmarksAnalyzer/src/main/kotlin/main.kt

@@ -129,7 +129,7 @@ fun mergeReportsWithDetailedFlags(reports: List<BenchmarksReport>) =
         }
 
 fun main(args: Array<String>) {
-    class Summary: Subcommand("summary") {
+    class Summary: Subcommand("summary", "Output summary information") {
         val exec by option(ArgType.Choice(listOf("samples", "geomean")),
                 description = "Execution time way of calculation").default("geomean")
         val execSamples by option(ArgType.String, "exec-samples",