Add optdepends

Thanks ryuzy

.SRCINFO

@@ -1,7 +1,7 @@
 pkgbase = rauc
 	pkgdesc = RAUC controls the update process on embedded linux systems. It is both a target application that runs as an update client and a host/target tool that allows you to create, inspect and modify installation artifacts.
 	pkgver = 1.5.1
-	pkgrel = 1
+	pkgrel = 2
 	url = https://github.com/rauc/rauc
 	arch = i686
 	arch = x86_64
@@ -9,6 +9,8 @@ pkgbase = rauc
 	makedepends = python
 	depends = curl
 	depends = json-glib
+	optdepends = casync: Casync integration support
+	optdepends = squashfs-tools: Extract or print the info of a bundle
 	source = https://github.com/rauc/rauc/releases/download/v1.5.1/rauc-1.5.1.tar.xz
 	source = https://github.com/rauc/rauc/releases/download/v1.5.1/rauc-1.5.1.tar.xz.asc
 	validpgpkeys = 977843FD5C3EBF76BAD4008EA58CC53DBF05E090
@@ -16,4 +18,3 @@ pkgbase = rauc
 	sha256sums = SKIP
 
 pkgname = rauc
-

PKGBUILD

@@ -2,18 +2,22 @@
 
 pkgname=rauc
 pkgver=1.5.1
-pkgrel=1
+pkgrel=2
 pkgdesc="RAUC controls the update process on embedded linux systems. It is both a target application that runs as an update client and a host/target tool that allows you to create, inspect and modify installation artifacts."
 arch=('i686' 'x86_64')
 url="https://github.com/rauc/rauc"
 license=('GPL')
 depends=('curl' 'json-glib')
 makedepends=('python')
+optdepends=(
+  'casync: Casync integration support'
+  'squashfs-tools: Extract or print the info of a bundle'
+)
 source=(https://github.com/$pkgname/$pkgname/releases/download/v$pkgver/$pkgname-$pkgver.tar.xz
         https://github.com/$pkgname/$pkgname/releases/download/v$pkgver/$pkgname-$pkgver.tar.xz.asc)
 sha256sums=('d4ea009ce702bcb083d942398ccfedec959c6bbb7adc0fd77ae9314ce11d9d91'
             'SKIP')
-validpgpkeys=('977843FD5C3EBF76BAD4008EA58CC53DBF05E090')
+validpgpkeys=('977843FD5C3EBF76BAD4008EA58CC53DBF05E090')  # Jan Lübbe <jlu@pengutronix.de>
 
 build() {
   cd $srcdir/$pkgname-$pkgver