Add loguru thirdparty metadata.

vtkm/thirdparty/loguru/update.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+set -e
+set -x
+shopt -s dotglob
+
+readonly name="loguru"
+readonly ownership="Loguru Upstream <kwrobot@kitware.com>"
+readonly subtree="vtkm/thirdparty/$name/vtkm$name"
+readonly repo="https://gitlab.kitware.com/third-party/$name.git"
+readonly tag="for/vtk-m"
+readonly paths="
+loguru.hpp
+README.md
+"
+
+extract_source () {
+    git_archive
+}
+
+. "${BASH_SOURCE%/*}/../update-common.sh"