* Added the topic Evaluating the clustering
How can we evaluate the clustering algorithms, based on analyzing our results.
* Fixed grammar and put in second person
* Translate challenge subtitles and example challenge text to Spanish
* Corrected errors in syntax and punctuation
* Multiple corrections of it/s to its plus other grammar corrections
* Correction and added paragraph to CSS Flex article
* Corrected my own typo
* Corrected capitalization, American spellings and typos