add hints for disk encryption

content/blog/ovh-pca-backupninja-duplicity.md

@@ -12,7 +12,7 @@ OVH provides a cheap way for longterm storing backup data, the Public Cloud Arch
 - Enable email sending for backup status mails by [installing a mta](/msmtp-on-debian/).
 - Install system dependencies
   - `apt install librsync-dev gpg backupninja`
-- Make sure to have disk encryption enabled for all files containing **secrets**
+- Make sure to have disk encryption enabled for all files containing **secrets**. Ex. with [luks](https://gitlab.com/cryptsetup/cryptsetup) or [gocryptfs](https://nuetzlich.net/gocryptfs/)
 
 
 #### GPG