README: show how to actually show the notes

I think we should extend the official docs that are part of systemd
with similar examples too, but it's reasonable to have the example here
in any case.

Author: keszybz

README.md

@@ -10,15 +10,95 @@ binary was compiled.
 See [Package Metadata for Core Files](https://systemd.io/ELF_PACKAGE_METADATA/)
 for the overview and details.
 
-The new `--package-metadata` option provided by `bfd`, `gold`, `mold`, and `lld` is used.
+When building binaries, the `--package-metadata` option provided by
+`bfd`, `gold`, `mold`, and `lld` shall be used to inject the metadata
+into the binary.
 
-It also provides scripts to extract and display `.note.dlopen` ELF notes
-that are used to describe libraries loaded via `dlopen(3)`.
+### Displaying package notes
+
+Raw:
+```console
+$ objdump -j .note.package -s /usr/bin/ls
+
+/usr/bin/ls:     file format elf64-x86-64
+
+Contents of section .note.package:
+ 03cc 04000000 7c000000 7e1afeca 46444f00  ....|...~...FDO.
+ 03dc 7b227479 7065223a 2272706d 222c226e  {"type":"rpm","n
+ 03ec 616d6522 3a22636f 72657574 696c7322  ame":"coreutils"
+ 03fc 2c227665 7273696f 6e223a22 392e342d  ,"version":"9.4-
+ 040c 372e6663 3430222c 22617263 68697465  7.fc40","archite
+ 041c 63747572 65223a22 7838365f 3634222c  cture":"x86_64",
+ 042c 226f7343 7065223a 22637065 3a2f6f3a  "osCpe":"cpe:/o:
+ 043c 6665646f 72617072 6f6a6563 743a6665  fedoraproject:fe
+ 044c 646f7261 3a343022 7d000000           dora:40"}...
+```
+
+Pretty:
+```console
+$ systemd-analyze inspect-elf /usr/bin/ls
+           path: /usr/bin/ls
+        elfType: executable
+elfArchitecture: AMD x86-64
+
+           type: rpm
+           name: coreutils
+        version: 9.4-7.fc40
+   architecture: x86_64
+          osCpe: cpe:/o:fedoraproject:fedora:40
+        buildId: 40e5a1570a9d97fc48f5c61cfb7690fec0f872b2
+```
+
+## `dlopen()` metadata
+
+This package also provides scripts to extract and display
+`.note.dlopen` ELF notes that are used to describe libraries loaded via `dlopen(3)`.
 
 See [`dlopen()` Metadata for ELF Files](https://systemd.io/ELF_DLOPEN_METADATA/)
 for the overview and details.
 
+### Displaying `dlopen()` notes
+
+Raw:
+```console
+$ objdump -j .note.dlopen -s /usr/lib64/systemd/libsystemd-shared-257.so
+
+/usr/lib64/systemd/libsystemd-shared-257.so:     file format elf64-x86-64
+
+Contents of section .note.dlopen:
+ 0334 04000000 8e000000 0a0c7c40 46444f00  ..........|@FDO.
+ 0344 5b7b2266 65617475 7265223a 22627066  [{"feature":"bpf
+ 0354 222c2264 65736372 69707469 6f6e223a  ","description":
+ 0364 22537570 706f7274 20666972 6577616c  "Support firewal
+ 0374 6c696e67 20616e64 2073616e 64626f78  ling and sandbox
+ 0384 696e6720 77697468 20425046 222c2270  ing with BPF","p
+ 0394 72696f72 69747922 3a227375 67676573  riority":"sugges
+ 03a4 74656422 2c22736f 6e616d65 223a5b22  ted","soname":["
+ 03b4 6c696262 70662e73 6f2e3122 2c226c69  libbpf.so.1","li
+ 03c4 62627066 2e736f2e 30225d7d 5d000000  bbpf.so.0"]}]...
+ 03d4 04000000 9e000000 0a0c7c40 46444f00  ..........|@FDO.
+...
+```
+
+Pretty:
+```console
+$ dlopen-notes /usr/lib64/systemd/libsystemd-shared-257.so
+# /usr/lib64/systemd/libsystemd-shared-257.so
+[
+  {
+    "feature": "bpf",
+    "description": "Support firewalling and sandboxing with BPF",
+    "priority": "suggested",
+    "soname": [
+      "libbpf.so.1",
+      "libbpf.so.0"
+    ]
+  },
+...
+```
+
 ## Requirements
 * binutils (>= 2.39)
 * mold (>= 1.3.0)
 * lld (>= 15.0.0)
+* python (>= 3.8)