Add warning for pre scan hook

Add a warning to clarify how to handle special pre scan requirement, like
gcc-10 has, since its source code is shipped in tarballs.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>

content/guides/component_guide.md

@@ -580,6 +580,12 @@ When such a situation arises, it is the responsibility of the submitter to
 perform the review of the license scan results and make updates to the package
 if necessary.
 
+{{% notice warning %}}
+Some packages like `gcc-10` require extra steps before the license scan:
+in this case, the package can provide a `debian/apertis/pre-scan-hook`
+executable script to run arbitrary preparation steps.
+{{% /notice %}}
+
 When the license scan mistakenly identifies a file as being under an incorrect
 license, or fails to process it correctly, there are three ways to fix this: