Add README on API usage

README

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+# go-pkparse-server
+
+`go-pkparse-server` is a multi-generational pokemon parser written in Go.
+
+
+### API Usage
+
+##### `POST /parse`
+
+Query Params:
+
+| Param | Required | Description                                     |
+| ---   | ---      | ---                                             |
+| pkmn  | ✔️        | One more pk7 files uploaded in a multipart form |
+
+Response:
+
+| Param          | Description                                            |
+| ---            | ---                                                    |
+| pokedex_number | National pokedex number of the pokemon                 |
+| nickname       | The UTF-16LE encoded nickname of the pokemon           |
+| raw_nickname   | Base 64 encoded byte string of the pokemon's nickname  |
+| raw_pokemon    | Base 64 encoded byte string of the entire pokemon data |
+
+Sample request and response:
+
+`curl -X POST http://localhost:8080/parse -F "pkmn=/path/to/thefile.pk7" -F "pkmn=/path/to/anotherfile.pk7" -H "Content-Type: multipart/form-data"`:
+```
+{
+   [
+      {
+         "nickname" : "R\u0000a\u0000t\u0000i\u0000c\u0000a\u0000t\u0000e\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000",
+         "pokedex_number" : 20,
+         "raw_nickname" : "UgBhAHQAaQBjAGEAdABlAAAAAAAAAAAA",
+         "raw_pokemon" : "ewMXgQAA3QEUAAAAbaoyREAfAAAvBAAAQ1aIAxISAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAFIAYQB0AGkAYwBhAHQAZQAAAAAAAAAAAAAApAB1AVMBngAKDxQPAAAAAAAAAAAAAAAAAAA8/P8XUABQAG8AcgBnAAAAAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAARgAAAAAAAAAAAAAAAABQAFAAbwByAGcAAAAAAAAAAAAAAAAAAAAAAEYAAAAAAAAAAAARCxIAAADKAAQUACEBAgACAAAAAA=="
+      },
+      {
+         "nickname" : "P\u0000i\u0000k\u0000a\u0000c\u0000h\u0000u\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000",
+         "pokedex_number" : 25,
+         "raw_nickname" : "UABpAGsAYQBjAGgAdQAAAAAAAAAAAAAA",
+         "raw_pokemon" : "wJsMkgAAN4IZAAAA0qVgJQAAAAAJAQAA7DtV5QAJAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAFAAaQBrAGEAYwBoAHUAAAAAAAAAAAAAAAAA8QFVABgB5wAPDw8PAAAAAFUAYgBXAGEAAAAWYq41UABQAG8AcgBnAAAAAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAARgAAAAAAAAAAAAAAAABBAHMAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAEYAAAAAAAAAAAARChAAAABBnAQBAB9OAAICAAAAAA=="
+      }
+   ]
+}
+```
+
+Sample error response:
+
+| Param | Description              |
+| ---   | ---                      |
+| error | description of the error |
+
+Example error:
+`curl -X POST http://localhost:8080/parse -F "pkmn=/path/to/an/invalidfile.pk7" -H "Content-Type: multipart/form-data"`:
+```
+{
+  "error": "Invalid length for generation 7 pokemon: 229 bytes"
+}
+```
+