feat: add installation process for zsh (#7)

Author: renancaraujo

.gitignore

@@ -4,4 +4,6 @@
 .dart_tool/
 .packages
 build/
-pubspec.lock
+pubspec.lock
+
+coverage/

.idea/.gitignore

@@ -0,0 +1,5 @@
+/// Contains the functions related to the installation file
+library install;
+
+export 'src/install/install_completion.dart';
+export 'src/install/shell_completion_installation.dart';

.idea/cli_completion.iml

@@ -0,0 +1,20 @@
+/// {@template completion_installation_exception}
+/// Describes an exception during the installation of completion scripts.
+/// {@endtemplate}
+class CompletionInstallationException implements Exception {
+  /// {@macro completion_installation_exception}
+  CompletionInstallationException({
+    required this.message,
+    required this.rootCommand,
+  });
+
+  /// The error message for this exception
+  final String message;
+
+  /// The command for which the installation failed.
+  final String rootCommand;
+
+  @override
+  String toString() => 'Could not install completion scripts for $rootCommand: '
+      '$message';
+}