Add certificate files for NSS AIA fetching unittest

net/data/ssl/certificates/README

Index: net/data/ssl/certificates/README
diff --git a/net/data/ssl/certificates/README b/net/data/ssl/certificates/README
index e0f22a2e711aa91f9b4bfdcc3cf347c7de48bbd1..e4e7e6498a3d025c681d296b95b2c3ff7558c941 100644
--- a/net/data/ssl/certificates/README
+++ b/net/data/ssl/certificates/README
@@ -183,3 +183,13 @@ unit tests.
      The .pem versions contain just the certs, while the .p12 versions contain
      both the cert and a private key, since there are multiple ways to import
      certificates into NSS.
+
+- aia-cert.pem
+- aia-intermediate.der
+- aia-root.pem
+     A certificate chain which we use to ensure AIA fetching works correctly
+     when using NSS to verify certificates (which uses our HTTP stack).
+     aia-cert.pem has a caIssuers that points to "aia-test.invalid" as the URL
+     containing the intermediate, which can be served via a URLRequestFilter.
+     aia-intermediate.der is stored in DER form for convenience, since that is
+     the form expected of certificates discovered via AIA.