readme: Add Joakim as a Nordic maintainer

Add Joakim Andersson as a new Nordic maintainer and remove the rest of
the Nordic maintainers.

Sebastian will be taking a sabbatical and Joakim will be taking over.

Change-Id: I7306caa38476ff1a67c918ddb9e5780e25cebd48
Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>
diff --git a/docs/contributing/maintainers.rst b/docs/contributing/maintainers.rst
index c73933f..c013a20 100644
--- a/docs/contributing/maintainers.rst
+++ b/docs/contributing/maintainers.rst
@@ -158,21 +158,9 @@
 Nordic Semiconductor Platforms
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Ioannis Glaropoulos
-    :email: `ioannis.glaropoulos@nordicsemi.no <ioannis.glaropoulos@nordicsemi.no>`__
-    :github: `ioannisg <https://github.com/ioannisg>`__
-
-Andrzej Głąbek
-    :email: `andrzej.glabek@nordicsemi.no <andrzej.glabek@nordicsemi.no>`__
-    :github: `anangl <https://github.com/anangl>`__
-
-Øyvind Rønningstad
-    :email: `oyvind.ronningstad@nordicsemi.no <oyvind.ronningstad@nordicsemi.no>`__
-    :github: `oyvindronningstad <https://github.com/oyvindronningstad>`__
-
-Sebastian Bøe
-    :email: `sebastian.boe@nordicsemi.no <sebastian.boe@nordicsemi.no>`__
-    :github: `SebastianBoe <https://github.com/SebastianBoe>`__
+Joakim Andersson
+    :email: `joakim.andersson@nordicsemi.no <joakim.andersson@nordicsemi.no>`__
+    :github: `joerchan <https://github.com/joerchan>`__
 
 
 Nuvoton Platform: