Added immutable oses' notes to the knowledge base

knowledge base/fedora silverblue.md

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+# Fedora Silverblue
+
+## TL;DR
+
+Changes to the base layer are executed in a new bootable filesystem root. This means that the system must be rebooted after a package has been layered.
+
+```shell
+# Check for available upgrades.
+rpm-ostree upgrade --check
+
+# Upgrade the system.
+rpm-ostree upgrade
+
+# Install packages.
+rpm-ostree install kmod-nvidia xorg-x11-drv-nvidia
+
+# Override packages.
+rpm-ostree override replace \
+  local/path/to/podman-3.1.2-1.fc34.x86_64.rpm \
+  https://kojipkgs.fedoraproject.org/packages/podman/3.1.2/1.fc34/x86_64/podman-plugins-3.1.2-1.fc34.x86_64.rpm
+
+# Remove packages.
+# Packages will still exist in the undelying base layer, but will not appear
+# in the booted root.
+rpm-ostree override remove nano
+
+# Rollback.
+rpm-ostree rollback
+
+# Make changes to the kernel's boot arguments.
+rpm-ostree kargs \
+  --append=rd.driver.blacklist=nouveau \
+  --append=modprobe.blacklist=nouveau \
+  --append=nvidia-drm.modeset=1
+
+# Preview changes on the current filesystem.
+rpm-ostree ex apply-live
+```
+
+## Package layering
+
+Package layering works by modifying your Silverblue installation by extending the packages from which Silverblue is composed.
+
+Using package layering creates a new _deployment_, or bootable filesystem root which **does not** affect your current root. This means that the system must be rebooted after a package has been layered.
+
+If you don't want to reboot your system to switch to the new deployment, you can use `rpm-ostree ex apply-live` to update the current filesystem and be able to see the changes from the new deployment. It's generally expected that you use package layering sparingly, and use [flatpak]s and [toolbox].
+
+## Further readings
+
+- [User guide]
+- [Flatpak]
+- [Toolbox]
+
+[flatpak]: flatpak.md
+[toolbox]: toolbox.md
+
+[user guide]: https://docs.fedoraproject.org/en-US/fedora-silverblue/