maintiain.md added more info

docs/MAINTAIN.md

@@ -5,3 +5,12 @@
 a file <family>.cmake must be added to the folder cmake/stm32
 This file containes the differents devices and the regex used to parse them.
 It also give information on the RAM and CCRAM available
+
+## Add family to list of know families
+
+Update the list `STM32_SUPPORTED_FAMILIES_LONG_NAME` located in the cmake/stm32/common.cmake file
+
+
+## Add family to CI
+
+Update the cmake.yml workflow file to include the new family