Add pre-commit-hook for formatting source (#4)

* Add pre-commit-hook for formatting source

This commit is to add the pre-commit hook which format source code
of csharp and vb.
It is used the command "dotnet format".

* Modify indent

This commit is to modify indent space of id.
It need 3 spaces.

* Add argument of files

This commit is to add the argument "--files" which set formatting
file path.

.pre-commit-hooks.yaml

@@ -0,0 +1,5 @@
+-   id: dotnet-format
+    name: dotnet-format
+    entry: dotnet format --files
+    language: system
+    files: '\.(cs|vb)$'