chore: fix some markdown style issues

Author: fgreinacher

README.md

@@ -3,11 +3,13 @@
 [![Codacy Badge](https://api.codacy.com/project/badge/Grade/2e777fa545c94767acccd6345b1ed9b7)](https://app.codacy.com/gh/System-IO-Abstractions/System.IO.Abstractions?utm_source=github.com&utm_medium=referral&utm_content=System-IO-Abstractions/System.IO.Abstractions&utm_campaign=Badge_Grade_Dashboard)
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-### Just like `System.Web.Abstractions`, but for `System.IO`. Yay for testable IO access!
+> ***Just like `System.Web.Abstractions`, but for `System.IO`. Yay for testable IO access!***
 
 At the core of the library is `IFileSystem` and `FileSystem`. Instead of calling methods like `File.ReadAllText` directly, use `IFileSystem.File.ReadAllText`. We have exactly the same API, except that ours is injectable and testable.
 
-    dotnet add package System.IO.Abstractions
+```shell
+dotnet add package System.IO.Abstractions
+```
 
 ```csharp
 public class MyComponent
@@ -40,7 +42,9 @@ public class MyComponent
 
 The library also ships with a series of test helpers to save you from having to mock out every call, for basic scenarios. They are not a complete copy of a real-life file system, but they'll get you most of the way there.
 
-    dotnet add package System.IO.Abstractions.TestingHelpers
+```shell
+dotnet add package System.IO.Abstractions.TestingHelpers
+```
 
 ```csharp
 [Test]