V3 Migration Guide

[mmmarcos]

[NicoTuxx]

• [x] Improve "Customer registration" section: (improve content, add screenshots, make specific use cases for monthly subscription vs custom order)
• [x] Improve "Parsec v3 installation" section (improve content, add screenshots)
• [x] Improve "Create first organization" section for monthly subscription use case (improve content, add screenshots)
• [x] Create the equivalent section for the custom order use case
• [x] Improve "Migrate data" section (improve content, add screenshots)
• [x] Improve "Unsubscribe" section for monthly subscription use case (improve content, add screenshots)
• [x] Create the equivalent section ("What to do on old version now?") for the custom order use case
• [x] Create an english version of this document
• [x] Eventually create 2 versions, one for monthly sub and one for on-premise
• [x] Replace Parsec Share with Parsec

[mmmarcos]

Migration Guide is finished.