Add help messages to show_source and show_doc commands (#887)

* Add help message to the show_source command

* Add help message to the show_doc command

Author: st0012

lib/irb/command/show_doc.rb

@@ -15,7 +15,21 @@ def transform_args(args)
       end
 
       category "Context"
-      description "Enter the mode to look up RI documents."
+      description "Look up documentation with RI."
+
+      help_message <<~HELP_MESSAGE
+        Usage: show_doc [name]
+
+        When name is provided, IRB will look up the documentation for the given name.
+        When no name is provided, a RI session will be started.
+
+        Examples:
+
+          show_doc
+          show_doc Array
+          show_doc Array#each
+
+      HELP_MESSAGE
 
       def execute(*names)
         require 'rdoc/ri/driver'

lib/irb/command/show_source.rb

@@ -8,7 +8,21 @@ module IRB
   module Command
     class ShowSource < Base
       category "Context"
-      description "Show the source code of a given method or constant."
+      description "Show the source code of a given method, class/module, or constant."
+
+      help_message <<~HELP_MESSAGE
+        Usage: show_source [target] [-s]
+
+          -s  Show the super method. You can stack it like `-ss` to show the super of the super, etc.
+
+        Examples:
+
+          show_source Foo
+          show_source Foo#bar
+          show_source Foo#bar -s
+          show_source Foo.baz
+          show_source Foo::BAR
+      HELP_MESSAGE
 
       class << self
         def transform_args(args)