Add the Revision field to third_party/fiat/README.chromium

This is copied over from the METADATA file, since Chromium's
infrastructure currently requires some duplicate work.

Bug: 347861602
Change-Id: I21ae055454c6dbe721ea99a4609d8144dd7846ad
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/69407
Auto-Submit: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

third_party/fiat/README.chromium

diff --git a/third_party/fiat/README.chromium b/third_party/fiat/README.chromium
index fe48544..fdf28a4 100644
--- a/third_party/fiat/README.chromium
+++ b/third_party/fiat/README.chromium
@@ -2,6 +2,7 @@
 Short Name: fiat-crypto
 URL: https://github.com/mit-plv/fiat-crypto
 Version: git (see METADATA)
+Revision: 6ccc6638716d4632304baf1adbb5c47c3a12ea6f
 License: MIT
 License File: LICENSE
 Security Critical: yes