please add quick documentation on pandas timestamp values of month, day of week
Pandas appears to use values for timestamp fields where 1 = January, 2 = February, etc., (vs. 0 = January) and 0 = Monday, 1 = Tuesday, 2 = Wednesday, 3 = Thursday, 4 = Friday, 5 = Saturday, 6 = Sunday. (vs. weekday numbering that starts with 1 instead of 0, or Sunday instead of Monday.)

```
dec31 = pd.Timestamp('2013-12-30 00:00:00')
dec31.weekday()
```

prints 0 in my system (Mac OSX + pandas 0.12.0)

This convention doesn't appear to be in the documentation + it would really help as it is one of several possibilities.
