python-dev + libi2c-dev remark & typo in filename

If python-dev is missing during installation of wiringPi, you'll get an error. If libi2c-dev is missing the python examples from this repo just don't work without an error message (so difficult to debug).

Typo in alphabet_text.py file name.
Merge pull request #5 from pe7er/patch-1

python-dev + libi2c-dev remark & typo in filename