spell checking my-first-couchdb-plugin's README

this pull request only fix spelling mistakes, but there's a part I would like to improve also

the opening note of the plugin README says:

"NOTE: This is incomplete, barely tested, works only with the 1867-feature-plugin branch of Apache CouchDB and expects that you understand some Erlang. This is mostly for early review, but if you are daring, you can learn someting already :)"

the branch name may be outdated since this works on 1.5.0, also the incomplete, barely tested part seems outdated, maybe "this feature is considered alpha/beta/subject to change"?

can you recommend a better warning note?