improve documentation

include/SPERR3D_Stream_Tools.h

@@ -34,12 +34,13 @@ class SPERR3D_Stream_Tools {
   // return an object of `SPERR3D_Stream_Header`.
   auto get_stream_header(const void*) const -> SPERR3D_Header;
 
-  // Function that reads in portions of a bitstream to facilitate progressive access.
+  // Function that reads in portions of a file only to facilitate progressive access.
+  // (This function does not read the whole file.)
   auto progressive_read(std::string filename, unsigned pct) const -> vec8_type;
 
-  // Function that truncates a bitstream to facilitate progressive access.
-  //    Note on `stream_len`: it does not to be the full length of the original bitstream, rather,
-  //    it can be just long enough for the requested truncation:
+  // Function that truncates a bitstream in the memory to facilitate progressive access.
+  //    Note on `stream_len`: it does not need to be the full length of the original bitstream,
+  //    rather it can be just long enough for the requested truncation:
   //  - one chunk: (full_bitstream_length * percent + 64) bytes.
   //  - multiple chunks: probably easier to just use the full bitstream length.
   auto progressive_truncate(const void* stream, size_t stream_len, unsigned pct) const -> vec8_type;