Doc: Add Linux as a supported platform for MCUs

Fixes: QTCREATORBUG-28551
Change-Id: I179e84bef57370f6c7616236aff33a969bc3bb17
Reviewed-by: Timo Aarnipuro <timo.aarnipuro@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

doc/qtcreator/src/overview/creator-only/creator-supported-platforms.qdoc

@@ -21,7 +21,7 @@
             \li {3,1} Development Platform
         \header
             \li \l Linux
-            \li \l macOS
+            \li \l \macos
             \li \l Windows
         \row
             \li \l Android
@@ -50,7 +50,7 @@
             \li
         \row
             \li \l{Microcontroller Units (MCU)}{MCUs}
-            \li
+            \li \image ok.png
             \li
             \li \image ok.png
         \row