docs: Add a short explanation for each sorting algorithm

To make the tool more educational, we should display a brief explanation of the algorithm that is currently selected in the dropdown. This helps users understand what they are visualizing.

Task:

Use an st.expander component in the sidebar, titled "About This Algorithm".

Inside the expander, write a simple if/elif/else block that checks which algorithm is selected.

Based on the selection, display a 1-2 sentence explanation of that algorithm. For example, if "Bubble Sort" is selected, show something like: "Bubble Sort is a simple sorting algorithm that repeatedly steps through the list, compares adjacent elements and swaps them if they are in the wrong order."

Write a similar short explanation for all 5-6 algorithms in the project.