Punctuation, grammar and <title> changes. 

I added header tags to index.html along with title tags so Bitcoin is clearly described on Google. I chose the title "Bitcoin - Open-source P2P Digital Currency" because it describes Bitcoin clearly and concisely and that's what the definition of Bitcoin is on the front-page. In other words, people will know exactly what Bitcoin is when it shows up on Google.

I also made minor grammatical and punctuation fixes: A colon before the list of features, a hyphen in "open-source", two hyphens in "peer-to-peer" and I changed "and a software" to "and software".

I don't think this should be a controversial addition. Please alert me to any errors you may find. Thank you!