Explain usage of -j1 option

[fhg-isi]

Suggestion:

In the getting started part of the documentation, simplify start command to

projects/technology-data % snakemake

instead of

projects/technology-data % snakemake -j1

or explain its relevance, for example:

(The -j1 option ensures subsequent job execution to .... Also see snakemake command line options.