docs: Display version and build time

This information is important so people know what version the
documentation they are looking at was built from.

docs/conf.py

 import os
 import sys
 import shutil
+import subprocess
+import time
 
 # Configuration file for the Sphinx documentation builder.
 #
@@ -14,6 +16,14 @@ project = 'flow3r'
 copyright = '2023'
 author = 'ccc'
 
+# The full version, including alpha/beta/rc tags
+release = (
+    subprocess.check_output(["git", "describe", "--tags", "--long", "--always"]).decode().strip()
+)
+release += "\n"
+release += time.strftime("%F %R")
+version = release
+
 # -- General configuration ---------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration