Include the policy document for the most recent FIPS validation.

NIST publishes the PDFs of the security policy documents (although the
latest one is still missing). We include the docx sources to help others
who might be doing a rebrand certification of BoringCrypto.

Change-Id: I5c1511d53ec1d09d257d3aab1301486c364b660b
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/51505
Reviewed-by: David Benjamin <davidben@google.com>

crypto/fipsmodule/FIPS.md

@@ -12,7 +12,7 @@ BoringCrypto has undergone the following validations:
 1. 2018-07-30: certificate [#3318](https://csrc.nist.gov/Projects/Cryptographic-Module-Validation-Program/Certificate/3318), [security policy](/crypto/fipsmodule/policydocs/BoringCrypto-Security-Policy-20180730.docx) (in docx format).
 1. 2019-08-08: certificate [#3678](https://csrc.nist.gov/Projects/Cryptographic-Module-Validation-Program/Certificate/3678), [security policy](/crypto/fipsmodule/policydocs/BoringCrypto-Security-Policy-20190808.docx) (in docx format).
 1. 2019-10-20: certificate [#3753](https://csrc.nist.gov/Projects/Cryptographic-Module-Validation-Program/Certificate/3753), [security policy](/crypto/fipsmodule/policydocs/BoringCrypto-Android-Security-Policy-20191020.docx) (in docx format).
-1. 2021-01-28: certificate [#4156](https://csrc.nist.gov/Projects/Cryptographic-Module-Validation-Program/Certificate/4156).
+1. 2021-01-28: certificate [#4156](https://csrc.nist.gov/Projects/Cryptographic-Module-Validation-Program/Certificate/4156), [security policy](/crypto/fipsmodule/policydocs/BoringCrypto-Android-Security-Policy-20210319.docx) (in docx format).
 
 ## Running ACVP tests