Prepare ZenUML community question and answers

Questions from StackOverflow:

• How to increase the space between participants in a ZenUML sequence diagram?

  • Question: https://community.atlassian.com/t5/Confluence-questions/How-to-increase-the-space-between-participants-in-a-ZenUML/qaq-p/1524463#M194095, 4 Nov

  • Answer: @Peng Xiao

• Insert a line between two element using css(https://stackoverflow.com/questions/58210665/insert-a-line-between-two-element-using-css)

  • Question: Planned to be asked by Rong Hu

URL for ZenUML community in Atlassian:

https://community.atlassian.com/t5/tag/zenuml/tg-p