docs: support python3 to generate docs (#801)

Co-authored-by: Bu Sun Kim <8822365+busunkim96@users.noreply.github.com>
diff --git a/describe.py b/describe.py
index e36db53..1887dc2 100755
--- a/describe.py
+++ b/describe.py
@@ -348,7 +348,10 @@
     html = document_collection(resource, path, root_discovery, discovery)
 
     f = open(os.path.join(FLAGS.dest, path + "html"), "w")
-    f.write(html.encode("utf-8"))
+    if sys.version_info.major < 3:
+        html = html.encode("utf-8")
+
+    f.write(html)
     f.close()
 
     for name in dir(resource):
@@ -450,7 +453,10 @@
                 markdown.append("\n")
 
             with open("docs/dyn/index.md", "w") as f:
-                f.write("\n".join(markdown).encode("utf-8"))
+                markdown = "\n".join(markdown)
+                if sys.version_info.major < 3:
+                    markdown = markdown.encode("utf-8")
+                f.write(markdown)
 
         else:
             sys.exit("Failed to load the discovery document.")