Add support for building with Podman

For those users who have both Docker and Podman installed, Docker will be used
by default unless the new "-e" option is used to specify which container engine
to use.

For those users who only have Podman installed, the script will use it without
having to specify a container engine.

README.md

@@ -4,7 +4,8 @@ This repository contains the source to build a Debian package for [alacritty](ht
 
 ## Usage
 
-If you have [Docker](https://www.docker.com/) installed locally, just run the following:
+If you have [Docker](https://www.docker.com/) or [Podman](https://podman.io/)
+installed locally, just run the following:
 
 ```bash
 user@hostname$ ./build.sh

build.sh

@@ -6,7 +6,16 @@ IMAGE="debian:bullseye-slim"
 TARGET="$(dirname "$0" | xargs realpath)"
 VERSION="v0.10.1"
 
-while getopts "v:i:h" opt
+if hash docker; then
+    ENGINE="docker"
+elif hash podman; then
+    ENGINE="podman"
+else
+    echo "ERROR: A supported container engine was not found!"
+    exit 1
+fi
+
+while getopts "v:i:e:h" opt
 do
     case "$opt" in
         v)
@@ -15,8 +24,11 @@ do
         i)
             IMAGE="$OPTARG"
             ;;
+        e)
+            ENGINE="$OPTARG"
+            ;;
         h)
-            echo "Usage: $0 [-i image] [-v version]"
+            echo "Usage: $0 [-i image] [-v version] [-e docker|podman]"
             exit 0
             ;;
         *)
@@ -26,7 +38,7 @@ do
 done
 
 main() {
-    docker run --rm --name alacritty-build-$$ \
+    ${ENGINE} run --rm --name alacritty-build-$$ \
                     --volume "$TARGET:/target" \
                     --workdir /target \
                     --env "VERSION=$VERSION" \