Cleanup readme

[Lex-2008]

first mention features/benefits:

• intellectual cleanup - main differentiator (I haven't seen it anywhere else)
  • starts deleting old files only when you're running out of disk space
  • prioritises hourly, daily, weekly, monthly backups ("daily" backup is state of backup dir at midnight, "monthly" - at midnight of first day of the month, etc) - so you have same number of daily backups as monthly
    • actually based not on number of backups, but their age - so before deleting a backup which was made 4 months ago, it will delete a backup which was made 5 days ago
• all features of rsync (since it's most often used for file transfer)
  • incremental backup - transfers only changed files, keeping history of several versions
  • remote backup
    • from multiple remote systems to single backup server
    • minor requirements to remote systems - directory with valuable data should be made available to backup server via any of the following means:
      • either via rsync server which is configured and running
      • or as shared folder
      • or via SSH access
      • exotic methods are also possible (like using external hard drive to backup air-gapped remote systems)
    • "pull" remote sync - if a remote system is compromised - it can't wipe backups (it can fill your backups with garbage, however - but that's true for any backup system)
    • read-only access from backup server to remote systems - if backup server is compromised - it can't wipe other systems (it can wipe your backups, however - but that's true for any backup system which doesn't use write-once medium like CD-R)
  • transparent protection against network transfer errors (when backing up from rsync server) - if a file is damaged due to network fluke, it will be retransferred
  • filtering of files to backup based on their path/name/ext
• lack of vendor lock-in - not using proprietary file format
  • all files in backup are stored as plain files
  • you can access them using any standard file manager
  • it will be more correct after maintain yesterday/last week/last hour views #36 is implemented - since currently files are renamed
• easy to navigate WebUI
  • restore any file or whole dir
  • password-protect any dir
  • remotely trigger backups
• parity files to protect against bit rot
• scheduled backup (scheduled manually via cron)
• encryption (configured manually via encfs)

then installation on all platforms

• debian/ubuntu, centos/rhel
• basically, prepend $package_manager install to first two lines of https://github.com/Lex-2008/backup3#requirements

then configuration (simple/advanced usage), WebUI, and all other complications can be moved to a separate "extra features" file