Add the program version via 'nvd --version' and the man page.

src/nvd

@@ -48,6 +48,8 @@ from pathlib import Path
 from subprocess import PIPE
 from typing import Dict, List, Optional, Tuple, Union
 
+NVD_VERSION = "0.1.0"
+
 USE_COLOUR = False
 
 SGR_RESET = 0
@@ -588,6 +590,12 @@ def parse_args():
         epilog="See the nvd(1) manual page for more information.",
     )
 
+    parser.add_argument(
+        "--version",
+        action="version",
+        version=f"nvd {NVD_VERSION}",
+    )
+
     parser.add_argument(
         "--color",
         default="auto",

src/nvd.1

@@ -1,4 +1,4 @@
-.TH nvd 1 2021-05-16 nvd "User Commands"
+.TH nvd 1 2021-05-16 nvd-0.1.0 "User Commands"
 .SH NAME
 nvd \- Nix/NixOS package version diff tool
 .SH SYNOPSIS