Improve metadata of blindsend project on github

Currently "About" = "Blindsend project". It is not very descriptive as it appears in search results on github. 

I suggest to improve the metadata of the project, in the following way.

let About = "Easy-to-use tool for private, end-to-end encrypted file exchange"

Tag the project with tags related to: privacy, compliance, gdpr, encryption, file-exchange