Add the runrom crate and the vnf library

The vnf library supports the runrom crate and they both combined enable
users to "run" a ROM file. This is basically an emulator, but with two
key differences:

1. It is to be run programatically. That is, you are not expected to
   play games with this, but to run code by steps, start at a given
   address, run a function, etc.
2. It is headless: there are no graphics displayed on screen, nor sound
   being delivered.

Thus, the target for both these things are developers, not players. This
way developers can validate code paths without needing a full blown
emulator. You can write tests with this and be able to run some checks
as part of your testing infrastructure.

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

1 files changed, 32 insertions, 0 deletions

diff --git a/crates/runrom/README.md b/crates/runrom/README.md
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+This is yet another NES/Famicom emulator. Only this time around it's
+specifically tailored to NES/Famicom developers, not players.
+
+First of all, the `vnf` library used for this binary exposes the virtual machine
+with a proper interface. This way, you can run ROM files programmatically. Then,
+`runrom` is just a wrapper on top of this library with a set of options that
+toggle certain features from it. This is a nice thing to have if you don't need
+to write very specific conditions with a tailored program. Second of all,
+`runrom` runs with no graphics nor sound. That is, it runs headless. Thus, it
+can be run on your testing infrastructure, so you can run continuous integration
+on critical paths from your games.
+
+## Basic usage
+
+You can run a ROM file by simply:
+
+```
+$ runrom <your-game-path>/game.nes
+```
+
+This will display all of the instructions being run. By default it will run from
+the reset vector. You can change that with the `-s/--start` option, which
+accepts a 16-bit address from where to start execution.
+
+That being said, most of the times you want to test a specific function. For
+that, you can toggle the `-f/--function` option, which tells `runrom` that the
+address is just a function and, whenever a top-level `rts`/`rti` instruction is
+found, then execution can be halted.
+
+Moreover, you may also find interesting the `-d/--dump-memory` option, which
+will display a summary of memory addresses which have been updated along
+execution, and some statistics about them.