add delta install script

.config/yadm/bootstrap.d/install-delta

@@ -0,0 +1,38 @@
+#!/bin/bash
+
+set -eu
+
+source "${BOOTSTRAP_LIB}/helpers"
+
+VERSION="0.13.0"
+INSTALL_DIR="${HOME}/.local/bin"
+INSTALLED_VERSION=""
+
+if [[ -x "$(command -v delta)" ]]; then
+  INSTALLED_VERSION="$(delta --version | grep -o '[0-9.]\+')"
+fi
+
+if [[ "$VERSION" == "$INSTALLED_VERSION" ]]; then
+  echo "Delta version ${VERSION} already installed."
+  exit 0
+fi
+
+echo "Installing delta version ${VERSION}..."
+
+URL="https://github.com/dandavison/delta/releases/download/${VERSION}/delta-${VERSION}-x86_64-unknown-linux-gnu.tar.gz"
+
+echo "Downloading from ${URL}..."
+TARGET="$(download "$URL")"
+
+if [[ -f "${INSTALL_DIR}/delta" ]]; then
+  echo "Removing old delta command..."
+  rm -f "${INSTALL_DIR}/delta"
+fi
+
+echo "Unpacking delta command to ${INSTALL_DIR}..."
+mkdir -p "${INSTALL_DIR}"
+tar --directory="${INSTALL_DIR}" --strip-components 1 -xf "${TARGET}" "delta-${VERSION}-x86_64-unknown-linux-gnu/delta"
+chmod +x "${INSTALL_DIR}/delta"
+
+echo "Removing ${TARGET}..."
+rm -f "${TARGET}"