feature<Preference>: query git version after selecting git path

src/Commands/Version.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace SourceGit.Commands {
+    /// <summary>
+    ///     检测git是否可用，并获取git版本信息
+    /// </summary>
+    public class Version : Command {
+        const string GitVersionPrefix = "git version ";
+        public string Query() {
+            Args = $"--version";
+            var result = ReadToEnd();
+            if (!result.IsSuccess || string.IsNullOrEmpty(result.Output)) return null;
+            var version = result.Output.Trim();
+            if (!version.StartsWith(GitVersionPrefix, StringComparison.Ordinal)) return null;
+            return version.Substring(GitVersionPrefix.Length);
+        }
+    }
+}