extended description

[MAHANTH-wq]

Floyd warshall algorithm uses dynamic programming approach sentence is been added

• [x] I have read freeCodeCamp's contribution guidelines.
• [x] My pull request has a descriptive title (not a vague title like Update index.md)
• [x] My pull request targets the master branch of freeCodeCamp.
• [x] None of my changes are plagiarized from another source without proper attribution.
• [x] My article does not contain shortened URLs or affiliate links.

Closes #XXXXX

[MAHANTH-wq]

I'm new here if i do any mistakes kindly let me know ,I'll be happy to learn.