crypto/internal/boring: add dev.boringcrypto README.md text

Add the text from dev.boringcrypto's README making clear what
this code is and that it is unsupported.

Change-Id: Ie49e8ccff10436f5d27ed422f159b4899193c9a5
Reviewed-on: https://go-review.googlesource.com/c/go/+/460515
Reviewed-by: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>

1 files changed, 21 insertions, 1 deletions

diff --git a/src/crypto/internal/boring/README.md b/src/crypto/internal/boring/README.md
index ffacd341c8..ec02786d96 100644
--- a/src/crypto/internal/boring/README.md
+++ b/src/crypto/internal/boring/README.md
@@ -1,3 +1,21 @@
+We have been working inside Google on a fork of Go that uses
+BoringCrypto (the core of [BoringSSL](https://boringssl.googlesource.com/boringssl/))
+for various crypto primitives, in furtherance of some work related to FIPS 140.
+We have heard that some external users of Go would be
+interested in this code as well, so we have published this code
+here in the main Go repository behind the setting GOEXPERIMENT=boringcrypto.
+
+Use of GOEXPERIMENT=boringcrypto outside Google is _unsupported_.
+This mode is not part of the [Go 1 compatibility rules](https://go.dev/doc/go1compat),
+and it may change incompatibly or break in other ways at any time.
+
+To be clear, we are not making any statements or representations about
+the suitability of this code in relation to the FIPS 140 standard.
+Interested users will have to evaluate for themselves whether the code
+is useful for their own purposes.
+
+---
+
 This directory holds the core of the BoringCrypto implementation
 as well as the build scripts for the module itself: syso/*.syso.
 
@@ -16,4 +34,6 @@ For the arm64 build to run on an x86 system, you need
 
 to allow the x86 kernel to run arm64 binaries via QEMU.
 
-See build.sh for more details.
+See build.sh for more details about the build.
+
+