Add nightly build support to installation script

Previously, the release version could be specified as an argument to the script, but it didn't support installing the
nightly. Since beta testers should always use the latest nightly, an easy method for grabbing it before starting test
work will be useful.

Author: per1234

Diff for: docs/installation.md

@@ -18,8 +18,8 @@ curl -fsSL https://raw.githubusercontent.com/arduino/arduino-lint/main/etc/insta
 If you would like to use the `arduino-lint` command from any location, install arduino-lint to a directory already in
 your `PATH` or add the arduino-lint installation path to your `PATH` environment variable.
 
-If you want to download a specific arduino-lint version, for example `0.9.0`, pass the version number as a parameter
-like this:
+If you want to download a specific arduino-lint version, for example `0.9.0` or `nightly-latest`, pass the version
+number as a parameter like this:
 
 ```
 curl -fsSL https://raw.githubusercontent.com/arduino/arduino-lint/main/etc/install.sh | sh -s 0.9.0

Diff for: etc/install.sh

@@ -139,7 +139,17 @@ downloadFile() {
 	else
 		ARDUINO_LINT_DIST="${PROJECT_NAME}_${TAG}_${OS}_${ARCH}.tar.gz"
 	fi
-	DOWNLOAD_URL="https://downloads.arduino.cc/${PROJECT_NAME}/${ARDUINO_LINT_DIST}"
+
+	# Support specifying nightly build versions (e.g., "nightly-latest") via the script argument.
+	case "$TAG" in
+	nightly*)
+		DOWNLOAD_URL="https://downloads.arduino.cc/${PROJECT_NAME}/nightly/${ARDUINO_LINT_DIST}"
+		;;
+	*)
+		DOWNLOAD_URL="https://downloads.arduino.cc/${PROJECT_NAME}/${ARDUINO_LINT_DIST}"
+		;;
+	esac
+
 	ARDUINO_LINT_TMP_FILE="/tmp/$ARDUINO_LINT_DIST"
 	echo "Downloading $DOWNLOAD_URL"
 	httpStatusCode=$(getFile "$DOWNLOAD_URL" "$ARDUINO_LINT_TMP_FILE")