docs: Make sure we run mkosi genkey before everything else

Otherwise other commands might fail saying the keys don't exist
yet.

docs/HACKING.md

@@ -39,6 +39,7 @@ chance that your distribution's packaged version of mkosi will be too old.
 Then, you can build, run and test systemd executables as follows:
 
 ```sh
+$ mkosi -f genkey                                  # Generate signing keys once.
 $ mkosi -f sandbox -- meson setup -Dbpf-framework=disabled build # bpftool detection inside mkosi sandbox is broken on Ubuntu Noble and older
 $ mkosi -f sandbox -- meson compile -C build
 $ mkosi -f sandbox -- build/systemctl --version
@@ -48,7 +49,6 @@ $ mkosi -f sandbox -- meson test -C build          # Run the unit tests
 To build and boot an OS image with the latest systemd installed:
 
 ```sh
-$ mkosi -f genkey                                  # Generate signing keys once.
 $ mkosi -f sandbox -- meson compile -C build mkosi # (re-)build the OS image
 $ mkosi boot                                       # Boot the image with systemd-nspawn.
 $ mkosi vm                                         # Boot the image with qemu.
@@ -64,8 +64,8 @@ $ git clone https://github.com/systemd/systemd.git
 $ cd systemd
 $ git checkout -b <BRANCH>                         # where BRANCH is the name of the branch
 $ $EDITOR src/core/main.c                          # or wherever you'd like to make your changes
-$ mkosi -f sandbox -- meson setup build            # Set up meson
 $ mkosi -f genkey                                  # Generate signing keys once.
+$ mkosi -f sandbox -- meson setup build            # Set up meson
 $ mkosi -f sandbox -- meson compile -C build mkosi # (re-)build the test image
 $ mkosi vm                                         # Boot the image in qemu
 $ git add -p                                       # interactively put together your patch