shorten startup massage to make it less confusing

[ablaette]

Currently:

polmineR is throttled to use 2 cores as required by CRAN Repository Policy. To get full performance:

• Use n_cores <- parallel::detectCores() to detect the number of cores available on your machine
• Set number of cores using options('polmineR.cores' = n_cores - 1) and data.table::setDTthreads(n_cores - 1)

Better:
data.table 1.14.8 using 2 threads (see ?getDTthreads). Latest news: r-datatable.com

[ChristophLeonhardt]

I think that the current startup message is good. It points to ?polmineR in which a comprehensive list of options is presented.

However, while this provides a great overview about these options, I am wondering whether users which arrive there from the startup message and expect a guide on how to "optimize performance" will find what they are looking for. In particular, there are no suggestions about which option to set and how to set it.

Maybe the example snippets which were included in the start up message earlier could be included in the documentation shown with ?polmineR, either in the examples themselves or the "details" section?