doc: add doc about unsupported platform warning

docs/advanced_usages/custom-tests.md

@@ -283,6 +283,13 @@ In addition to the required `AntaTest.anta_tests` decorator, ANTA offers a set o
 
 - `anta.decorators.deprecated_test`: Use this to log a message of WARNING severity when a test is deprecated.
 - `anta.decorators.skip_on_platforms`: Use this to skip tests for functionalities that are not supported on specific platforms.
+
+    !!! info "Warning "
+        If a device returns an error for a specific command, and the error message contains `not supported on this hardware platform`, a warning will be displayed because the decorator `anta.decorators.skip_on_platforms` is missing on the test for a specific platform.
+        ```
+        WARNING  Test VerifyAdverseDrops has been skipped because it is not supported on cEOSLab, please open a GitHub issue.
+        ```
+
 - `anta.decorators.check_bgp_family_enable`: Use this to skip tests when a particular BGP address family is not configured on the device.
 
 !!! warning