Updated build instructions with the ones found in README.

PKGBUILD

@@ -0,0 +1,32 @@
+# Emiliano Vavassori <syntaxerrormmm@gmail.com>
+
+pkgname=zsync2-git
+pkgver=2.0.0a
+pkgrel=1
+pkgdesc="A file transfer program that's able to connect to rsync servers"
+arch=(x86_64)
+url="https://github.com/AppImage/zsync2"
+license=("custom:Artistic")
+provides=(zsync2)
+conflicts=(zsync2)
+depends=(curl)
+makedepends=(cmake git gnutls openssl zlib)
+source=(git+$url.git)
+b2sums=('SKIP')
+
+prepare() {
+  cd ${pkgname/-git/}
+  git submodule update --init
+}
+
+build() {
+  cmake -B build ${pkgname/-git/} \
+    -DUSE_SYSTEM_CURL=1 -DBUILD_CPR_TESTS=0 \
+    -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_INSTALL_LIBDIR=lib
+  make -C build
+}
+
+package() {
+  make -C build DESTDIR="$pkgdir" install
+  install -Dm644 ${pkgname/-git/}/COPYING "$pkgdir/usr/share/licenses/$pkgname/COPYING"
+}