Add example images for all filters and different sigma values

A2/images/coins/log_3.jpeg

A2/images/coins/prewitt.jpeg

A2/images/coins/roberts.jpeg

A2/images/coins/sobel.jpeg

A2/images/edit.jpeg

A2/images/immunohistochemistry/kirsch.jpeg

A2/images/immunohistochemistry/log_1.jpeg

A2/images/immunohistochemistry/log_1_5.jpeg

A2/images/immunohistochemistry/log_2.jpeg

A2/images/immunohistochemistry/log_3.jpeg

A2/images/immunohistochemistry/prewitt.jpeg

A2/images/immunohistochemistry/roberts.jpeg

A2/images/immunohistochemistry/sobel.jpeg

A2/images/original.jpeg