Document Silkaj usage

• Installation
• CLI basics: group of commands, general and command specific options
• Authentication: already in account_storage, move it somewhere else?
• Account storage support: authentication, revoca... (#477)
• wot commands:
  • lookup
  • status
  • certify
  • membership
  • revocation
• money commands:
  • transfer
    • transfer to multiple recipients
    • transfer with recipients from a file
  • balance
  • history
• license
• blockchain commands:
  • info
  • blocks
• How to
  • How to create a wallet
  • How to become member
• FAQ

To be put later on the website Set up new website structure with MkDocs (#433)