refactor: archive generated documentation

This change ensures that compiled Sphinx documentation is archived and
downloadable from the job artefacts.

Signed-off-by: Chris Kay <chris.kay@arm.com>
Change-Id: I6ad1669a1eabe1af447ceaeef8ba347cade7975f
diff --git a/group/tf-l1-check-docs/build-docs:nil b/group/tf-l1-check-docs/build-docs:nil
index 02d845d..c6b4665 100644
--- a/group/tf-l1-check-docs/build-docs:nil
+++ b/group/tf-l1-check-docs/build-docs:nil
@@ -12,3 +12,7 @@
 
 	targets="doc" set_tf_build_targets
 }
+
+post_tf_build() {
+	mv "$tf_root/docs/build" "$archive"
+}