Auto merge of #2203 - arcalinea:2142_security_log_message, r=daira

Add message directing users to security guide

Addresses #2142, which was blocking on updates to zcash/support/security.html. That page has now been added, so this message directing users to the site can be included.

It displays in the zcash-cli --help and --version message text, and on the zcashd metrics screen.

src/util.h

@@ -142,6 +142,9 @@ void ShrinkDebugFile();
 void runCommand(const std::string& strCommand);
 const boost::filesystem::path GetExportDir();
 
+/** Returns privacy notice (for -version, -help and metrics screen) */
+std::string PrivacyInfo();
+
 /** Returns licensing information (for -version) */
 std::string LicenseInfo();