Implement review notes backup guide

[steersbob]

File: backup_guide.md
Commit: 5be4c2c
Review date: April 15 2021
Tech: Tested on laptop with kubuntu 20.04 LTS and Brewblox with build date: 2021-04-07T14:53:23.863Z. Spark (service: spark-one) with Fermentation Fridge wizard blocks (standard). Spark is powered & connected over USB. Spark simulation (spark-sim) was added as extra service with HERMS setup from wizard (standard).

l3 "..or simply be prepared for possible SD card failures of your Pi."

Backup test - situation: brewblox service is up and UI is shown in browser:

1. brewblox-ctl backup save - success
2. Delete test layout
3. brewblox-ctl backup load - success
4. Test layout is back! All links to blocks are broken though. I see a lot of red exclamation marks, see LoadBackupBlocksNotConnected.png. No wonder, the Spark (spark-one) and the simulation spark (spark-sim) are connected but both hold not a single block - see BlockListEmpty.png. Refreshing the page (F5) fixes the issue.
   Conclusion: should I only backup and load after brewblox-ctl down? Maybe add a line to the guide to close the UI before backup load, or refresh after.
5. brewblox-ctl update - works, already on latest version

l20 "..and run brewblox-ctl update to migrate.."

l37 Why are only Exported Spark blocks in the backup? And why are block names exported separately? Confusing... I can imagine this is because of the technical details of how Brewblox is set up but I do not fully understand that yet. Maybe a high-level explanation is better here.

l42 Ok, what does this mean? What can I do with my backup and what do I need to save separately? What will I lose when I don't? What is in the docker images anyway?

I think this guide is better oriented to the 'novice user'. I don't know what is in .env, forgot what is in docker-compose.yml -something related to connecting and discovering Sparks?- and I've never heard about Datastore databases. All I care about is my Dashboards, widgets, Blocks and Spark configurations. Maybe add a link to the Developer Docs where the real details are discussed for the tech-savvy ones. Add a story about how to save and load your history data too. I presume this is done through CSV? Or is there another way? Can you import history data back into Brewblox from CSV files? I am still curious about what is in those Docker images too...

l50 grab the .zip-file in your brewblox\backup\ directory to save it for future use, or move it to your new Pi.

l55 "..migrate your configuration to the latest version." Why is this? Will brewblox-ctl update trigger setting conversions too? Why don't you want to do this before loading a backup? Curious..

l60 "On Linux you can use cron.."