dnscrypt-proxy: add /etc/dnscrypt-proxy.conf as configuration file

Since version 1.8.0, there is a proper configuration file at
/etc/dnscrypt-proxy.conf.

srcpkgs/dnscrypt-proxy/template

@@ -1,7 +1,7 @@
 # Template file for 'dnscrypt-proxy'
 pkgname=dnscrypt-proxy
 version=1.9.1
-revision=1
+revision=2
 build_style=gnu-configure
 makedepends="libsodium-devel"
 short_desc="DNS proxy that encrypts queries"
@@ -10,6 +10,7 @@ license="ISC"
 homepage="https://dnscrypt.org/"
 distfiles="https://download.dnscrypt.org/${pkgname}/${pkgname}-${version}.tar.gz"
 checksum=3a319e8bfff5ac15a1c5a80af71755380b1fb869cb8fd86b33b7ed928db65195
+conf_files="/etc/dnscrypt-proxy.conf"
 system_accounts="dnscrypt_proxy"
 
 post_install() {