build: add useful scripts for installing template

Can now install it locally (or anywhere else) quite easily. This is the first step for being able to auto create PRs when we do a release

scripts/setup

@@ -0,0 +1,37 @@
+# source this script to prepare some common environment variables
+
+# adapted from https://github.com/johannes-wolf/cetz/blob/35c0868378cea5ad323cc0d9c2f76de8ed9ba5bd/scripts/package
+# licensed under Apache License 2.0
+
+# Local package directories per platform
+if [[ "$OSTYPE" == "linux"* ]]; then
+  DATA_DIR="${XDG_DATA_HOME:-$HOME/.local/share}"
+elif [[ "$OSTYPE" == "darwin"* ]]; then
+  DATA_DIR="$HOME/Library/Application Support"
+else
+  DATA_DIR="${APPDATA}"
+fi
+
+function read-toml() {
+  local file="$1"
+  local key="$2"
+  # Read a key value pair in the format: <key> = "<value>"
+  # stripping surrounding quotes.
+  perl -lne "print \"\$1\" if /^${key}\\s*=\\s*\"(.*)\"/" < "$file"
+}
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")"; pwd -P)/.." # macOS has no realpath
+PKG_PREFIX="$(read-toml "$ROOT/typst.toml" "name")"
+VERSION="$(read-toml "$ROOT/typst.toml" "version")"
+
+function resolve-target() {
+  local target="$1"
+
+	if [[ "$target" == "@local" ]]; then
+		echo "${DATA_DIR}/typst/packages/local"
+	elif [[ "$target" == "@preview" ]]; then
+		echo "${DATA_DIR}/typst/packages/preview"
+	else
+		echo "$target"
+	fi
+}