Add explicit info about options to calibrate_carbon_bymonth() in vign…

…ette (a suggestion from Linnia Hawkins)

vignettes/example_workflow.Rmd

@@ -48,7 +48,7 @@ for (i in 1:length(fnames.out)) {
 }
 ```
 
-Two different methods to calibrate are available: a) a 'gain and offset' regression using 12CO2 and 13CO2 mole fractions (after Bowling et al. 2003) and b) a 'direct' linear regression of CO2 and d13C values to generate calibration transfer functions. The function 'calibrate_carbon_bymonth()' assumes you have vectors of: 1) input file names (fnames), 2) output file names (fnames.out), and 3) 4 letter NEON site codes corresponding to each entry in input file names (fnames). An example of code to generate these three vectors is provided below: 
+Two different methods to calibrate are available: a) a 'gain and offset' regression using 12CO2 and 13CO2 mole fractions (method = 'Bowling_2003', after Bowling et al. 2003) and b) a 'direct' linear regression of CO2 and d13C values to generate calibration transfer functions (method = 'linreg'). The function 'calibrate_carbon_bymonth()' assumes you have vectors of: 1) input file names (fnames), 2) output file names (fnames.out), and 3) 4 letter NEON site codes corresponding to each entry in input file names (fnames). An example of code to generate these three vectors is provided below: 
 
 ```{r, eval = FALSE}
 data.dir <- '/your/path/here/DP4_00200_001/'