Add Ruby Frankfurt Meetup events (ruby-conferences#613)

Author: marcoroth

_data/meetups.yml

@@ -61,6 +61,13 @@
   end_time: 20:00:00 CET
   url: https://www.meetup.com/polishrubyusergroup/events/298459627
 
+- name: Ruby Frankfurt Meetup - January 2024
+  location: Frankfurt am Main, Germany
+  date: 2024-01-30
+  start_time: 18:30:00 CET
+  end_time: 20:30:00 CET
+  url: https://www.meetup.com/frankfurt-ruby-meetup/events/298436132
+
 - name: "Ruby User Group Berlin: February Meetup 2024"
   location: Berlin, Germany
   date: 2024-02-01
@@ -250,6 +257,13 @@
   end_time: 19:00:00 EDT
   url: https://www.meetup.com/nyc-rb/events/299753087
 
+- name: Ruby Frankfurt Meetup - April 2024
+  location: Frankfurt am Main, Germany
+  date: 2024-04-16
+  start_time: 18:30:00 CEST
+  end_time: 20:30:00 CEST
+  url: https://www.meetup.com/frankfurt-ruby-meetup/events/299586276
+
 - name: Geneva.rb - Revisiting the Hotwire Landscape after Turbo 8 (Marco Roth)
   location: Geneva, Switzerland
   date: 2024-04-16