ruby, gem: update page; irb, rake: add page (#10412)

* gem: update page

* Use `snake_case` for placeholders
* Update the documentation URL

* ruby: move `irb` example to a separate page

* rake: add page

* ruby: reference other ruby-related pages

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* irb: standard input => `stdin` (#10436)

---------

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

pages/common/rake.md

@@ -0,0 +1,25 @@
+# rake
+
+> A Make-like program for Ruby.
+> Tasks for `rake` are specified in a Rakefile.
+> More information: <https://ruby.github.io/rake>.
+
+- Run the `default` Rakefile task:
+
+`rake`
+
+- Run a specific task:
+
+`rake {{task}}`
+
+- Execute `n` jobs at a time in parallel (number of CPU cores + 4 by default):
+
+`rake --jobs {{n}}`
+
+- Use a specific Rakefile:
+
+`rake --rakefile {{path/to/Rakefile}}`
+
+- Execute `rake` from another directory:
+
+`rake --directory {{path/to/directory}}`