ruby: 0000-fundamentals.rb: added regular expression notes
ruby: 0000-fundamentals.rb: added regular expression notes

This patch is created to include the ways to use regular expression
notes especially during string processing.

Signed-off-by: (Holloway) Chew, Kean Ho <bbd8faa40b0f348214bf4124b281a301299ba6dd@gmail.com>

josiahsoh/learning,josiahsoh/learning,hollowaykeanho/learning,hollowaykeanho/learning,josiahsoh/learning,hollowaykeanho/learning,hollowaykeanho/learning,hollowaykeanho/learning,josiahsoh/learning,josiahsoh/learning