[README] Add Usage section

Author: leptos-null

README.md

@@ -2,4 +2,49 @@
 
 `classdumpctl` is a command line tool to dump Objective-C class and protocol headers.
 
-classdumpctl is built on top of [ClassDumpRuntime](https://github.com/leptos-null/ClassDumpRuntime)
+`classdumpctl` is built on top of [ClassDumpRuntime](https://github.com/leptos-null/ClassDumpRuntime).
+
+### Usage
+
+`classdumpctl` is designed for 3 primary uses:
+
+- Inspecting a single class or protocol at a time
+  - use `-c <class name>` or `-p <protocol name>`
+  - the output will be colorized by default (see `-m`)
+  - you may need to specify `-i <path>` with the path to the library or framework containing the class or protocol if it's not already loaded
+- Dumping a single library or framework
+  - use `-i <path>` to specify the path to the binary
+  - use `-o <path>` to specify a directory to put the headers in
+- Dumping the entire `dyld_shared_cache`
+  - use `-a`
+  - use `-o <path>` to specify a directory to put the headers in
+  - uses concurrency to process all images in the shared cache quickly (see `-j`)
+
+It can also do more. See the full options listing below:
+
+```
+Usage: classdumpctl [options]
+Options:
+  -a, --dyld_shared_cache    Interact in the dyld_shared_cache
+                               by default, dump all classes in the cache
+  -l, --list                 List all classes in the specified image
+                               if specified with -a/--dyld_shared_cache
+                               lists all images in the dyld_shared_cache
+  -o <p>, --output=<p>       Use path as the output directory
+                               if specified with -a/--dyld_shared_cache
+                               the file structure of the cache is written to
+                               the specified directory, otherwise all classes found
+                               are written to this directory at the top level
+  -m <m>, --color=<m>        Set color settings, one of the below
+                               default: color output only if output is to a TTY
+                               never: no output is colored
+                               always: output to TTYs, pipes, and files are colored
+  -i <p>, --image=<p>        Reference the mach-o image at path
+                               by default, dump all classes in this image
+                               otherwise may specify --class or --protocol
+  -c <s>, --class=<s>        Dump class to stdout (unless -o is specified)
+  -p <s>, --protocol=<s>     Dump protocol to stdout (unless -o is specified)
+  -j <N>, --jobs=<N>         Allow N jobs at once
+                               only applicable when specified with -a/--dyld_shared_cache
+                               (defaults to number of processing core available)
+```