pyproject.toml: make pynrfjprog an optional dependencies

Author: lschuermann

pyproject.toml

@@ -16,14 +16,16 @@ dependencies = [
     "crcmod >= 1.7",
     "ecdsa >= 0.19.1",
     "pycryptodome >= 3.15.0",
-    "pynrfjprog >= 10.19.0",
     "pyserial >= 3.0.1",
     "siphash >= 0.0.1",
     "six >= 1.9.0",
     "toml >= 0.10.2",
     "tqdm >= 4.45.0 ",
     "questionary >= 1.10.0",
 ]
+optional-dependencies = [
+    "pynrfjprog >= 10.19.0",
+]
 
 [project.urls]
 Home = "https://github.com/tock/tockloader"