Add README.md for github.

Author: madler

README.md

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+Synopsis
+--------
+
+_sunzip_ is a streaming unzip utility. It will read a .zip file from stdin and
+decompress its contents into the current directory. Command line options allow
+specifying a different destination directory, overwriting existing files
+(normally prevented), and testing the contents of .zip file instead of writing
+the decompressed files.
+
+_sunzip_ can decompress methods 0 (stored), 8 (deflated), 9 (Deflate64), 10
+(DCL imploded), and 12 (bzip2). _sunzip_ handles Zip64 .zip files. It does not
+handle encrypted .zip files.
+
+Motivation
+----------
+
+Most unzip utilities require random access to the .zip file, since they first
+read the central directory at the end, and then use that to access the entries
+in the .zip file. Those utilities cannot accept a .zip file on a pipe. _sunzip_
+reads and processes the .zip file contents sequentially. The entry information
+in the central directory is applied to the already decompressed files when the
+central directory is read.
+
+Installation
+------------
+
+Compile and link with zlib, infback9.c and inftree9.c (found in zlib's contrib
+directory), blast.c (also in contrib), and libbz2. blast.c from zlib 1.2.9 or
+later must be used.
+
+Test
+----
+
+`cat any.zip | sunzip`
+
+License
+-------
+
+This code is under the zlib license, permitting free commercial use.