sanitycheck: add notes key to schema

Prior to addition of schema validation running sanitycheck
--generate-hw-map would preserve the value of any field in an existing
map that it didn't update.  These fields now cause a parsing error.
Add notes as an optional key where information relevant to the board
can be added to provide useful context (such as which serial port
corresponds to the console, or why a non-standard runner is required).

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>

doc/guides/test/sanitycheck.rst

@@ -573,3 +573,25 @@ and these tests will be executed on the boards that provide this fixture.
 
 .. figure:: fixtures.svg
    :figclass: align-center
+
+Notes
++++++
+
+It may be useful to annotate board descriptions in the hardware map file
+with additional information.  Use the "notes" keyword to do this.  For
+example::
+
+    - available: true
+      connected: false
+      fixtures:
+        - gpio_loopback
+      id: 000683290670
+      notes: An nrf5340pdk_nrf5340 is detected as an nrf52840dk_nrf52840 with no serial
+        port, and three serial ports with an unknown platform.  The board id of the serial
+        ports is not the same as the board id of the the development kit.  If you regenerate
+        this file you will need to update serial to reference the third port, and platform
+        to nrf5340pdk_nrf5340_cpuapp or another supported board target.
+      platform: nrf52840dk_nrf52840
+      product: J-Link
+      runner: jlink
+      serial: null

scripts/sanity_chk/hwmap-schema.yaml

@@ -12,6 +12,9 @@ sequence:
       "id":
         type: str
         required: true
+      "notes":
+        type: str
+        required: false
       "platform":
         type: str
         required: true