Fix links in README.md (#105)

Author: sawich

README.md

@@ -73,8 +73,8 @@ This *open-access* course is directed at those who are already familiar with C a
 | **21** | [**Performance Optimizations I**](21.Optimization_I.pdf) ([html](https://federico-busato.github.io/Modern-CPP-Programming/htmls/21.Optimization_I.html))                               | Ahmdal Law, Performance bounds, Architecture concepts (ILP, SIMD, etc.), Memory hierarchy         |
 | **22** | [**Performance Optimizations II**](22.Optimization_II.pdf) ([html](https://federico-busato.github.io/Modern-CPP-Programming/htmls/22.Optimization_II.html))                            | Arithmetic optimizations, Memory optimizations, etc.                                              |
 | **23** | [**Performance Optimizations III**](23.Optimization_III.pdf) ([html](https://federico-busato.github.io/Modern-CPP-Programming/htmls/23.Optimization_III.html))                         | Compiler optimizations, Profiling, Benchmarking tools                                             |
-| **24** | [**Software Design I**](24.Software_Deisgn_I.pdf) ([html](https://federico-busato.github.io/Modern-CPP-Programming/htmls/24.Software_Deisgn_I.html))                                   | Basic Concepts, Principles, Use cases                                                             |
-| **25** | [**Software Design II**](25.Software_Deisgn_II.pdf) ([html](https://federico-busato.github.io/Modern-CPP-Programming/htmls/25.Software_Deisgn_II.html))                                | Design Patterns and Idioms                                                                        |
+| **24** | [**Software Design I**](24.Software_Design_I.pdf) ([html](https://federico-busato.github.io/Modern-CPP-Programming/htmls/24.Software_Design_I.html))                                   | Basic Concepts, Principles, Use cases                                                             |
+| **25** | [**Software Design II**](25.Software_Design_II.pdf) ([html](https://federico-busato.github.io/Modern-CPP-Programming/htmls/25.Software_Design_II.html))                                | Design Patterns and Idioms                                                                        |
 
 ***ALL-IN-ONE BOOK***: [**modern-cpp.pdf**](modern-cpp.pdf) (could be a few commits behind), [html](https://federico-busato.github.io/Modern-CPP-Programming/htmls/modern-cpp.html)