chore: added pieces of information recovered due to a failed cfengine installation test

knowledge base/cfengine3.md

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+# CFEngine
+
+## Table of contents <!-- omit in toc -->
+
+1. [TL:DR](#tldr)
+1. [Installation](#installation)
+1. [Further readings](#further-readings)
+1. [Sources](#sources)
+
+## TL:DR
+
+| Command     | Configuration            |
+| ----------- | ------------------------ |
+| `cf-remote` | `~/.cfengine/cf-remote/` |
+
+```sh
+# List packages available for download.
+cf-remote list
+
+# Add hosts to groups.
+# Will allow to use groups in other commands.
+cf-remote save -H 'root@cfengine.lan' --role 'hub' --name 'hubs-group-name'
+cf-remote save -H 'user@client.lan' --role 'client' --name 'clients-group-name'
+
+# Show hosts spawned by `cf-remote` or added to it.
+cf-remote show
+cf-remote show --ansible-inventory
+
+# Get info about hosts.
+cf-remote info -H 'host-alias'
+
+# Bootstrap remote hosts.
+cf-remote install -B 'hub'
+cf-remote --log-level 'INFO' install -B 'hub'
+
+# Install a specific edition on remote hosts.
+cf-remote install -E 'community' -c 'client'
+cf-remote install -E 'enterprise' --hub 'hub'
+
+# Reset `cf-remote` settings.
+rm -r "${HOME}/.cfengine/cf-remote"
+
+# Print the contents of DB files.
+cf-check dump
+
+# Assess the health of one or more DB files.
+cf-check diagnose
+
+# Diagnose databases, then backup and delete any one found corrupted.
+cf-check repair
+```
+
+## Installation
+
+On the development machine:
+
+```sh
+pip3 install 'cfbs' 'cf-remote'
+cf-remote save -H 'root@cfengine.lan' --role 'hub' --name 'hub'
+cf-remote install --hub 'hub' --bootstrap 'hub'
+```
+
+## Further readings
+
+- [Website]
+- [Documentation]
+
+## Sources
+
+All the references in the [further readings] section, plus the following:
+
+<!-- project's references -->
+[documentation]: https://docs.cfengine.com/docs/master/
+[website]: https://cfengine.com/
+
+<!-- internal references -->
+[further readings]: #further-readings
+
+<!-- external references -->