add readme

README.md

@@ -0,0 +1,42 @@
+# hashstream
+
+A combined streaming hasher.
+
+Hashstream is designed for needing multiple different hash types from a single stream / file simultaneously.
+
+Hashstream does not perform any file IO on its own, it only reads and writes to stdio. You must pipe `|` or `<` redirect input to hashstream for processing.
+
+Useful for coordinating systems that provide different hashtypes for stored blobs.
+
+# Usage
+
+` dd if=/dev/zero bs=4M count=250 status=progress | hashstream --sha256 `
+` hashstream --all < /home/user/somefile.dat `
+
+```
+Usage: hashstream [OPTIONS]
+
+Options:
+      --all          Enable all hash types, can not be used with any other hash type flag [DEFAULT]
+      --sha256       SHA2-256
+      --sha3-256     SHA3-256
+      --sha1         SHA1
+      --crc32-iso    CRC_32_ISO_HDLC
+      --crc32-posix  CRC_32_CKSUM
+      --crc32-xfer   CRC_32_XFER
+      --blake256     Blake2b256
+      --blake512     Blake2b512
+      --blake3       Blake3
+      --md5          MD5
+  -h, --help         Print help
+  -V, --version      Print version
+
+```
+
+# TODO:
+
+ - Multithreading? Maybe higher performance for multiple hashes at same time? 
+ - More hash types? idk what else may be useful
+ - Passthrough processing? Maybe output hashes to stderr or socket / named pipe?
+ - More perf tuning? Is faster than `*sum` utils on Arch for me, but slower under Alma and MacOS...
+ - Polynym binary? i.e. like busybox, selects set of hashes based on binary / link name?