Update the README for open sourcing the project

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

1 files changed, 21 insertions, 1 deletions

diff --git a/README.md b/README.md
index 91d2ed7..4a74a66 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,21 @@
-Under development
+Utilities for NES/Famicom development. Note that this repository is under heavy
+development and it's **not** currently usable.
+
+## `nasm`
+
+`nasm` is an assembler specifically tailored for the NES/Famicom. You can simply
+run it like so:
+
+```
+$ cargo run --bin nasm <path-to-assembly-file>
+```
+
+By default it will assume the configuration for an `NROM` file, but this can be
+changed with the `-c/--configuration` flag, which accepts the following values:
+
+- `empty`: just `HEADER` and `CODE`. Useful for one-liners (e.g. "how is this
+  instruction encoded in binary?").
+- `nrom`: the default configuration. It has the following segments: `HEADER`,
+  `CODE`, `VECTORS`, and `CHARS`.
+- `nrom65`: same as `nrom` but it also has `STARTUP` for compatibility with the
+  default linker configuration from [cc65](https://github.com/cc65/cc65).