Document steps for setting up R environment

[kzollove]

Certain steps must be taken when setting up the R environment to download/upload/import sizeable geospatial data down from the original source, up to the postGIS database, and then back down to the users machine.

Some steps for setting up:

• change the java heap size that is allowed
• change the R system variable for memory allocation
• increase timeout from 60 to ~600

Could there be a utility function user runs to make all these changes?

[rtmill]

Connected to #8

DatabaseConnector function that is likely relevant:
https://github.com/OHDSI/DatabaseConnector/blob/6bdece864cfa9a5c9ea9b6d5473df4d2f8a30335/R/Sql.R#L28

And I forget the function name but there's a similar one for R system variables. Can do a check on both and give warnings with the package loads, or something similar