Michael joined as Celix committer (Jul 2020)

https://lists.apache.org/thread.html/r6ba8bc80f55d270318f7b46bf40199b458e76b0ed19085c8d8849a11%40%3Cdev.celix.apache.org%3E
diff --git a/source/contributing/volunteers.md b/source/contributing/volunteers.md
index 25b6e17..bdd53ad 100644
--- a/source/contributing/volunteers.md
+++ b/source/contributing/volunteers.md
@@ -32,3 +32,4 @@
 - Daan Fischer (dfischer at apache.org)
 - Roy Bulter (rbulter at apache.org)
 - Idzard Hoekstra (idzardh at apache.org)
+- Michael de Lang (oipo at apache.org)