Add "scrypt" to third_party for secure password hashes

third_party/scrypt/FORMAT

Index: third_party/scrypt/FORMAT
diff --git a/third_party/scrypt/FORMAT b/third_party/scrypt/FORMAT
new file mode 100644
index 0000000000000000000000000000000000000000..10f699d8ec833264676f8ff942c6ec6e150883bf
--- /dev/null
+++ b/third_party/scrypt/FORMAT
@@ -0,0 +1,18 @@
+scrypt encrypted data format
+----------------------------
+
+offset	length
+0	6	"scrypt"
+6	1	scrypt data file version number (== 0)
+7	1	log2(N) (must be between 1 and 63 inclusive)
+8	4	r (big-endian integer; must satisfy r * p < 2^30)
+12	4	p (big-endian integer; must satisfy r * p < 2^30)
+16	32	salt
+48	16	first 16 bytes of SHA256(bytes 0 .. 47)
+64	32	HMAC-SHA256(bytes 0 .. 63)
+96	X	data xor AES256-CTR key stream generated with nonce == 0
+96+X	32	HMAC-SHA256(bytes 96 .. 96 + (X - 1))
+
+AES256-CTR is computed with a 256-bit AES key key_enc, and HMAC-SHA256 is
+computed with a 256-bit key key_hmac, where
+  scrypt(password, salt, N, r, p, 64) == [key_enc][key_hmac]