Add installation page

modules/ROOT/nav.adoc

@@ -1,3 +1,4 @@
+* xref:installation.adoc[Installation]
 * xref:concepts.adoc[Flatpak Concepts]
 * xref:tutorial.adoc[Packaging Tutorial]
 * xref:in-depth.adoc[Packaging In Depth]

modules/ROOT/pages/installation.adoc

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+include::{partialsdir}/attributes.adoc[]
+
+
+= Installation
+
+== Setup on Fedora Linux
+
+Just install the `flatpak` package, if not already installed:
+
+ $ sudo dnf install flatpak
+
+(You may need to log out and log back in.)
+
+[NOTE]
+========
+On Fedora systems, installing the `flatpak` package also installs the `fedora-testing` remote, but in disabled state. To enable it, run:
+
+....
+$ flatpak remote-modify --enable fedora-testing
+....
+========
+
+== Setup on Other Systems
+
+First, install the `flatpak` package through your system's native package manager.
+
+Then, add the Fedora stable flatpak remote:
+
+ $ flatpak remote-add --title "Fedora Flatpaks" fedora oci+https://registry.fedoraproject.org
+
+Optionally, add the Fedora testing flatpak remote:
+
+ $ flatpak remote-add --title "Fedora Flatpaks (testing)" fedora-testing oci+https://registry.fedoraproject.org#testing
+
+== Usage
+
+If installation succeeded, you can now install runtimes, SDKs, or applications:
+
+ $ flatpak install fedora APP_ID
+
+Graphical package managers (such as GNOME Software or KDE Plasma Discover) also allow for installation of applications by selecting the "Fedora Flatpaks" software source.