python3-decouple: new package

Add a recipe for python-decouple: generic tool for separating settings
from code.

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-python/recipes-core/packagegroups/packagegroup-meta-python.bb

@@ -92,6 +92,7 @@ RDEPENDS:packagegroup-meta-python3 = "\
     python3-dbus-next \
     python3-dbussy \
     python3-decorator \
+    python3-decouple \
     python3-defusedxml \
     python3-dill \
     python3-diskcache \