[R][BACKPORT-2.3] update package description

## What changes were proposed in this pull request?

apache#23852

doesn't port cleanly to 2.3. we need this in branch-2.4 and branch-2.3

Closes apache#23861 from felixcheung/2.3rdesc.

Authored-by: Felix Cheung <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>

Author: felixcheung

R/pkg/DESCRIPTION

@@ -1,6 +1,8 @@
 Package: SparkR
 Type: Package
 Version: 2.3.4
+Title: R Front end for 'Apache Spark'
+Description: Provides an R Front end for 'Apache Spark' <https://spark.apache.org>.
 Authors@R: c(person("Shivaram", "Venkataraman", role = c("aut", "cre"),
                     email = "[email protected]"),
              person("Xiangrui", "Meng", role = "aut",