Merge bitcoin/bitcoin#30551: doc: mention optional dependencies (qrencode, zmq) in OpenBSD build docs

903def1ffd doc: mention optional dependencies (qrencode, zmq) in OpenBSD build docs (Sebastian Falbesoner)

Pull request description:

  The wording is taken from the FreeBSD build docs.

  Tested on OpenBSD 7.5. See the following links for the package names:
  - https://openbsd.app/?search=libqrencode
  - https://openbsd.app/?search=zeromq

  Thanks to hebasto for noticing that this was missing.

ACKs for top commit:
  maflcko:
    review ACK 903def1ffd
  hebasto:
    ACK 903def1ffd, I can successfully build with the `libqrencode` and `zeromq` packages on my OpenBSD 7.5 installation.

Tree-SHA512: 955e4892948a7703627d304a41a774f7cca0e4c672bdfa0edf531587d6970444aa49195b0f6f531ce375c8e7c2af6bbfa1a12e0612ae7a65f3e454fb17958672

doc/build-openbsd.md

@@ -66,6 +66,22 @@ Bitcoin Core includes a GUI built with the cross-platform Qt Framework. To compi
 pkg_add qtbase qttools
 ```
 
+###### libqrencode
+
+The GUI can encode addresses in a QR Code. To build in QR support for the GUI, install `libqrencode`. Skip if not using the GUI or don't want QR code functionality.
+```bash
+pkg_add libqrencode
+```
+---
+
+#### Notifications
+###### ZeroMQ
+
+Bitcoin Core can provide notifications via ZeroMQ. If the package is installed, support will be compiled in.
+```bash
+pkg_add zeromq
+```
+
 ## Building Bitcoin Core
 
 **Important**: Use `gmake` (the non-GNU `make` will exit with an error).