Merge branch '104-add-education-milestones-to-the-roadmap' into 'master'

Resolve "Add education milestones to the roadmap"

Closes #104

See merge request hifis/hifis.net!154

_roadmap/software/2021-02-26-tasks.md

+---
+date: 2021-02-26
+title: Tasks in February 2021
+service: software
+---
+
+## Publish training program for the first half of 2021 
+The education and training work package publishes the offered training events for the first half of 2021 on <https://software.hifis.net/events>.

_roadmap/software/2021-06-30-tasks.md

+---
+date: 2021-06-30
+title: Tasks in June 2021
+service: software
+---
+
+## Publish training program for the second half of 2021 
+The education and training work package publishes the offered training events for the second half of 2021 on <https://software.hifis.net/events>.