docs: tweak the man-page a bit to make the example more useful

The existing man-page is a bit misleading as it claims that the
command in the example will generate an image. Because osbuild
generates what is requested this is not actually true. This
commit tweaks the examples a bit to make them more useful. It
also fixes a numbering bug (we had two "Example 1").

It also tweaks the description of `fedora-boot.json` as it is no
longer fedora 34 but 38.

docs/osbuild.1.rst

@@ -125,10 +125,10 @@ produces no output:
     | # echo {} | osbuild -
     |
 
-Example 1: Build a Fedora 34 qcow2 image
-----------------------------------------
+Example 2: See pipeline IDs of a Fedora qcow2 image
+---------------------------------------------------
 
-To build a basic qcow2 image of Fedora 34, use:
+To inspect a basic qcow2 image of Fedora, use:
 
     |
     | # osbuild ./samples/fedora-boot.json
@@ -137,13 +137,31 @@ To build a basic qcow2 image of Fedora 34, use:
 The pipeline definition ``./samples/fedora-boot.json`` is provided in the
 upstream source repository of **osbuild**.
 
-Example 2: Run from a local checkout
+This will print out the pipeline IDs of the provided manifest but will
+not actually build anything because no artifact was requested. The pipeline
+IDs can then be passed to ``--export=`` to actually get the requested
+artifacts.
+
+
+Example 3: Build a Fedora qcow2 image
+-------------------------------------
+
+To build a basic qcow2 image of Fedora, use:
+
+    |
+    | # osbuild --output-dir ./out --export image  ./samples/fedora-boot.json
+    |
+
+Note that the command requires to be run as root. It will create an out/image
+directory and put the generated "disk.img" there.
+
+Example 4: Run from a local checkout
 ------------------------------------
 
 To run **osbuild** from a local checkout, use:
 
     |
-    | # python3 -m osbuild --libdir . samples/fedora-boot.json
+    | # python3 -m osbuild --libdir . --output-dir ./out --export image samples/fedora-boot.json
     |
 
 This will make sure to execute the **osbuild** module from the current