Added documentation for configuration of R script

docs/4-Editing-Rscript-and-Config.md

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+#Editing R script and config file
+
+In the current setup, the R script will generate config files for all possible soil and weather file combinations. More commonly, one would have a specific experimental design in mind. To avoid running a number of models that are not wanted, instead of using all possible ocmbinations, the experimental design can be loaded from a csv file. This csv file also needs to be saved in the working directory together with the config file template. 
+
+The csv file needs two columns, with Soil names in one column and weather files in another column. The easiest way to alter the R script is to remove the lines loading soil names and weather files (lines 6 and 7) as well as the lines that creates the experimental design (line 25) and loading the csv file with the experimental design by adding the following lines
+
+```r
+Des <- read.csv('CsvFileName.csv')
+colnames(Des) <- c('Var1', 'Var2')
+```
+
+If you instead wish to change different parameters (i.e., not only soil and weather) over the modelling iterations, the config file needs to be changed to have a generic name for the parameter you wish to change (Instructions on how to write an apsim config file is available at https://apsimnextgeneration.netlify.app/usage/editfile/), as well as its own column in the csv file (suggestedly named 'Var3' if you wish to keep the other two as well). The R script will also need to be updated to include this new variable. This is done by adding one extra line where the config files are created such as:
+
+```r
+Config <- gsub(pattern = 'VariableName', replacement = Des$Var3[i], Config)
+```
+Where VariableName should be replaced with the keyword written in the config file. 
+
+
+To to prevent files from being overwritten, Des$Var3 also needs to be added to the file name by changing the line
+
+```r
+ConfigFilePath <- paste0("./", Des$Var1[i], "_", Des$Var2[i], "ConfigFile.txt")
+```
+To 
+
+```r
+ConfigFilePath <- paste0("./", Des$Var1[i], "_", Des$Var2[i], "_", Des$Var3[i], "ConfigFile.txt")
+```
+