Replace an old README.chromium file with a plain README.md

This is a remnant of the move of the certificate verifier for Chromium
to BoringSSL.

Change-Id: I545d1422a193fac65ca3f078fd9ebe161cccd56c
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/77327
Commit-Queue: Bob Beck <bbe@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
Reviewed-by: Bob Beck <bbe@google.com>
diff --git a/pki/testdata/nist-pkits/README.chromium b/pki/testdata/nist-pkits/README.chromium
deleted file mode 100644
index 3f09e09..0000000
--- a/pki/testdata/nist-pkits/README.chromium
+++ /dev/null
@@ -1,20 +0,0 @@
-Name: NIST Public Key Interoperability Test Suite
-Short Name: NIST PKITS
-URL: http://csrc.nist.gov/groups/ST/crypto_apps_infra/pki/pkitesting.html
-Version: 1.0.1
-Date: 2011-04-14
-License: Public Domain: United States Government Work under 17 U.S.C. 105
-Shipped: no
-Security Critical: no
-
-Description:
-The Public Key Interoperability Test Suite (PKITS) is a comprehensive X.509
-path validation test suite that was developed by NIST in conjunction with BAE
-Systems and NSA.  The PKITS path validation test suite is designed to cover
-most of the features specified in X.509 and RFC 3280.
-
-Local Modifications:
-Only the certs/ and crls/ directories were extracted from PKITS_data.zip.
-
-pkits_testcases-inl.h is generated from the test descriptions in PKITS.pdf
-using generate_tests.py.
diff --git a/pki/testdata/nist-pkits/README.md b/pki/testdata/nist-pkits/README.md
new file mode 100644
index 0000000..c1e001e
--- /dev/null
+++ b/pki/testdata/nist-pkits/README.md
@@ -0,0 +1,7 @@
+# NIST Public Key Interoperability Test Suite
+
+This directory contains test data from the NIST [Public Key Interoperability Test Suite](http://csrc.nist.gov/groups/ST/crypto_apps_infra/pki/pkitesting.html) (NIST PKITS), version 1.0.1, fetched 2011-04-14. NIST PKITS test data is under public domain (United States Government Work under 17 U.S.C. 105). This directory is not included in BoringSSL when compiled and is only used for testing.
+
+Only the `certs/` and `crls/` directories were extracted from `PKITS_data.zip`.
+
+`pkits_testcases-inl.h` is generated from the test descriptions in `PKITS.pdf` using `generate_tests.py`.