Add info about what the lesson is not about in the first page for students

[agbeltran]

The instructor notes indicate that the lesson is not about data analysis but data organization (http://www.datacarpentry.org/spreadsheet-ecology-lesson/guide/).

I think this is useful information for students too, when listing the learning objectives on the main page (http://www.datacarpentry.org/spreadsheet-ecology-lesson/) to set the appropriate expectations.

[hoytpr]

Hi @agbeltran, It looks like this has been addressed in the lesson. Would you like me to close this or do have more you would like to add to the objectives?

[hoytpr]

Issue addressed. closing #205