update readme

Signed-off-by: Zen <[email protected]>

Author: desultory

readme.md

@@ -1,7 +1,68 @@
  ![Tests](https://github.com/desultory/pycpio/actions/workflows/unit_tests.yml/badge.svg)
 
-# pycpio
+# PyCPIO
 
-A library for working with CPIO files using python
+A library for creating CPIO files in Python.
 
-In active development
+Currently, the library only supports the New ASCII format, and xz compression
+
+This library is primary designed for use in [ugrd](https://github.com/desultory/ugrd) to create CPIO archives for use in initramfs.
+
+## Usage
+
+```
+  -h, --help            show this help message and exit
+  -d, --debug           enable debug mode (level 10)
+  -dd, --trace          enable trace debug mode (level 5)
+  -v, --version         print the version and exit
+  --log-file LOG_FILE   set the path to the log file
+  --log-level LOG_LEVEL
+                        set the log level
+  --log-time            enable log timestamps
+  --no-log-color        disable log color
+  -i INPUT, --input INPUT
+                        input file
+  -a APPEND, --append APPEND
+                        append to archive
+  --recursive RECURSIVE
+                        append to archive recursively
+  --relative RELATIVE   append to archive relative to this path
+  --absolute            allow absolute paths
+  --reproducible        Set mtime to 0, start inodes at 0
+  --rm RM, --delete RM  delete from archive
+  -n NAME, --name NAME  Name/path override for append
+  -s SYMLINK, --symlink SYMLINK
+                        create symlink
+  -c CHARDEV, --chardev CHARDEV
+                        create character device
+  --major MAJOR         major number for character/block device
+  --minor MINOR         minor number for character/block device
+  -u UID, --set-owner UID
+                        set UID on all files
+  -g GID, --set-group GID
+                        set GID on all files
+  -m MODE, --set-mode MODE
+                        set mode on all files
+  -z COMPRESS, --compress COMPRESS
+                        compression type
+  -o OUTPUT, --output OUTPUT
+                        output file
+  -l, --list            list CPIO contents
+  -p, --print           print CPIO contents
+  ```
+
+# Structure
+
+- `pycpio.header.cpioheader`: The class which represents a CPIO header
+  * Can be initialized from args for header fields, or bytes representing a header
+  * header types are defined in `pycpio.header.headers` (only the new ascii format is supported)
+- `pycpio.cpio.data`: The class which represents a CPIO data block
+  * Each CPIO object must have a header.
+  * Currently the follwing subtypes are supported:
+    - `file` : A regular file, or hardlink.
+    - `dir` : A directory
+    - `symlink` : A symbolic link
+    - `chardev` : A character device
+  * CPIO objects are collected in a `pycpio.cpio.archive` object
+    - The archive handles duplication, inode generation, name normalization, and other collection related tasks
+  * All CPIO object types can be initialized from args, bytes, or a file path