message: Updates primal's README file to include spatial indexes.
diff: -PRIMAL: Geomtric primitives and associated computational geometry tests {#primaltop}
  +PRIMAL: Geometric primitives and associated computational geometry tests {#primaltop}
  ========
  Primal provides several useful geometric primitive types (e.g. Point, BoundingBox, Triangles)
  and several computational geometry tests on these primitives (e.g. intersection, proximity, orientation).
  +
  +It also provides spatial acceleration data structures over collections of spatial objects (e.g. bounding volume hierarchy, uniform grid)
  