Document flags in README.md

Flags added: --kernel-order, --plain, --command (-c)

README.md

@@ -4,5 +4,14 @@
 #!/bin/sh
 stdgather INTEL_DEBUG=shaders,ann,hex,bat MESA_SHADER_CACHE_DISABLE=true ./main
 ```
+
+#### Flags
+##### `--kernel-order`
+Do not use multiple PTYs - let the kernel sort them out. See Issue #1.
+##### `--plain`
+Do not show any fancy timestamps, colors, etc.
+##### `-c` `--command`
+Stop parsing args and interpret the rest as a command (optional)
+
 ### Image
 ![Screenshot of the above command piped into neovim with the syntax highlighting](./pics/stdgather_demo.png)