[WIP] Update emojis and add readme

I added a README with instructions on how to use this project and updated the emojis to their newest masters.

If you allow me this comment: Wow, is this a big mess! C, Go and Python to generate some emojis o_O

README.md

+# Briar Spritegen
+
+Used for generating emojis for Briar.
+
+Forked from [github.com/mcginty/spritegen](https://github.com/mcginty/spritegen).
+
+## Dependencies
+
+* gcc
+* go
+* imagemagick
+* optipng
+
+## Preparation
+
+Clone [github.com/googlei18n/nototools](https://github.com/googlei18n/nototools).
+
+Follow [the installation instructions](https://github.com/googlei18n/nototools#installation).
+
+Run `make` in _noto-emoji_.
+
+Compile _spritegen_ by running `go build spritegen.go`.
+
+## Usage
+
+Execute `./generate-for-briar.sh`.
+
+## What do to next?
+
+When everything went well, you can go update
+the new emojis in Briar:
+[code.briarproject.org/briar/briar/tree/master/briar-android/src/main/assets](https://code.briarproject.org/briar/briar/tree/master/briar-android/src/main/assets)
+
+## License
+
+See [LICENSE.md](LICENSE.md) for more information.