Add package level documentation and citation information

Change-Id: I109311d37747d7c65bd7db893f10e25ebe432e3a
diff --git a/man/rderekovecs-package.Rd b/man/rderekovecs-package.Rd
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+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/rderekovecs-package.R
+\docType{package}
+\name{rderekovecs-package}
+\alias{rderekovecs}
+\alias{rderekovecs-package}
+\title{rderekovecs: DeReKoVecs API Client Package}
+\description{
+A client package that makes the 'DeReKoVecs' web service API accessible from R.
+}
+\seealso{
+Useful links:
+\itemize{
+  \item \url{https://korap.ids-mannheim.de/gerrit/plugins/gitiles/ids-kl/derekovecs}
+  \item \url{https://corpora.ids-mannheim.de/openlab/derekovecs}
+}
+
+}
+\author{
+\strong{Maintainer}: Marc Kupietz \email{kupietz@ids-mannheim.de}
+
+}
+\keyword{internal}