CI Docs: Archive Docs in Original Path

TF-M has tranferred to new build system.
Docs path is also different from the old one.

To keep the same url to generated docs,
which is needed by trustedfirmware.org,
docs path needs to be same to the old one.
So generated docs should be archived in original path.

Change-Id: I5ee710a8e3e1e5217af2e2a04e5f407757ec672b
Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
diff --git a/build-docs.sh b/build-docs.sh
index 44aa37d..a1f34e0 100755
--- a/build-docs.sh
+++ b/build-docs.sh
@@ -26,3 +26,6 @@
                  -DMCUBOOT_PATH=../../mcuboot
 cmake --build ./ -- tfm_docs_refman_html
 cmake --build ./ -- tfm_docs_userguide_html
+
+mkdir -p install/doc
+cp -r docs/* install/doc/