hwdef: add comments clarifying use of each of the minimize includes

libraries/AP_HAL_ChibiOS/hwdef/include/minimize_common.inc

@@ -1,3 +1,8 @@
+# this include file is used to remove features which will never be
+#  wanted on any low-flash board in our standard builds.  It is to be
+#  included by other minimize_*.inc files and not generally used
+#  otherwise.
+
 # disable emitting nice strings when activating RC channel aux functions:
 define AP_RC_CHANNEL_AUX_FUNCTION_STRINGS_ENABLED 0
 

libraries/AP_HAL_ChibiOS/hwdef/include/minimize_features.inc

@@ -1,3 +1,7 @@
+# this is an include file to be used on low-flash boards which are not
+#  generally used for FPV/OSD purposes.  Care must be taken to
+#  preserve existing features on these boards.
+
 include minimize_common.inc
 
 # remove various OSD features by default:

libraries/AP_HAL_ChibiOS/hwdef/include/minimize_fpv_osd.inc

@@ -1,3 +1,7 @@
+# this is an include file for low-flash boards typically used in
+# vehicles used for FPV/OSD flight.  These boards are unlikely to need
+# drivers for rare sensors and power systems.
+
 include minimize_common.inc
 
 define AP_OPTICALFLOW_ENABLED 0