Since Bitcoin has been around now for over seven years and has a $10 Billion+ market capitalization, just wanted to submit this PR for review to remove the mentioning in the opening paragraph of the README that states that it is "an experimental new digital currency" to instead read "a digital currency" (in case you all are OK w/ this).
Alternatively, if you all would like to revise further, please let me know and I will amend my commit, or feel free to close if it should be left unchanged. Thanks in advance for the review!