Rewrite About section

[bumbu]

About section should be rewritten. It should contain:

• This project was done for GitHub data challenge
• Which data is targeted in this project (issues)
• Which data parameters are taken into account:
  • Issues labels
  • Issues lifespan (open - close time)
  • Issues agglomeration (how many issues are open at the same time)
  • Other?
• Interesting data that can be found
  • Bigger are semicircles - longer it takes to close issues. So big semicircles are bad
  • There are periods of times when many issues are closed. It may be related to releases
  • Different issues proportions
  • Other?
• If an issues has few labels - each label weight one unit in stackedArea chart
• Other?