improve wording

git-svn-id: https://svn.r-project.org/R/trunk@65943 00db46b3-68df-0310-9c12-caf00c1e9a41
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git-svn-id: https://svn.r-project.org/R/trunk@65945 00db46b3-68df-0310-9c12-caf00c1e9a41
allow https:// URLs where supported
updates to description


git-svn-id: https://svn.r-project.org/R/trunk@65946 00db46b3-68df-0310-9c12-caf00c1e9a41