For the non thread-grouping paths, only the first (0th) OFI context
should be used for communication. Otherwise this would access a non existant
array item and cause segfault.
While at it, clarifiy some content regarding SEPs in README (Credit to Matias Cabral
for README edits).
Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@intel.com>