docs: clarify zero-copy where possible

Author: Lulzx

README.md

@@ -4,7 +4,7 @@ A PDF text extraction library written in Zig.
 
 ## Features
 
-- Memory-mapped file reading for efficient large file handling
+- Memory-mapped file reading, zero-copy where possible
 - Streaming text extraction with efficient arena allocation
 - Multiple decompression filters: FlateDecode, ASCII85, ASCIIHex, LZW, RunLength
 - Font encoding support: WinAnsi, MacRoman, ToUnicode CMap