message: fix positions docs
diff: //! Tantivy can (if instructed to do so in the schema) store the term positions in a given field.
  //! This position is expressed as token ordinal. For instance,
  -//! In "The beauty and the beast", the term "the" appears in position 0 and position 4.
  +//! In "The beauty and the beast", the term "the" appears in position 0 and position 3.
  //! This information is useful to run phrase queries.
  //!
  //! The [position](../enum.SegmentComponent.html#variant.Positions) file contains all of the
  //! bitpacked positions delta, for all terms of a given field, one term after the other.
  //!
  //! Each term is encoded independently.
  -//! Like for positing lists, tantivy relies on simd bitpacking to encode the positions delta in
  -//! blocks of 128 deltas. Because we rarely have a multiple of 128, a final block may encode the
  -//! remaining values variable byte encoding.
  +//! Like for posting lists, tantivy relies on simd bitpacking to encode the positions delta in
  +//! blocks of 128 deltas. Because we rarely have a multiple of 128, the final block encodes
  +//! the remaining values with variable int encoding.
  //!
  -//! In order to make reading possible, the term delta positions first encodes the number of
  -//! bitpacked blocks, then the bitwidth for each blocks, then the actual bitpacked block and finally
  +//! In order to make reading possible, the term delta positions first encode the number of
  +//! bitpacked blocks, then the bitwidth for each block, then the actual bitpacked blocks and finally
  //! the final variable int encoded block.
  //!
  //! Contrary to postings list, the reader does not have access on the number of positions that is
  