Clarify implementation assumptions in the docs

[davestewart]

It took me longer than I would have liked to get up and running with this lib:

• I wasn't sure where the files were saved
• I didn't understand how the data was serialised

Quite a lot of console.loging, searching through finder folders, etc

It would be nice the following were mentioned:

• './scratch/' is a process-relative folder (maybe just include the trailing slash?)
• data will be saved in individual named text files, one per key, i.e. ./scratch/value
• data should be processed using JSON.stringify / parse (the word "serialized" implies this might be done for you)

I know the docs mention "Fully implements the localStorage specfication" but it's not like I go to bed at night reading the specs.

Also:

• typo in "specfication" (missing i after the c)

Otherwise, thanks very much! Nice lib once up and running :)