Update lesson-1.md

Changed sentence 2 in ##Making your First Map to more accurately describe that this is an an aid + changed a preposition.

Changed sentence 3 in ##Making your First Map to have parallel verbs.

In ###Creating a Table changed the instructions to reflect a more logical order. Added em-dashes, rephrased sentences, corrected a pronoun.

Changed ###Starting with you visualization to ###Starting with Your Visualization to make it grammatically correct and reflect the capitalizations found in the other sections.  Added instructions re: where to click to look at other basemaps. Clarified what "adm0cap" means. Added more instructions for how to select your own markers.

I made so many changes after this that I think it's better if you just look at it as a whole; most changes were related to clarifying the instructions, very few were stylistic changes to the sentences.