add readme

README.md

@@ -0,0 +1,30 @@
+subscribe-bot
+=============
+
+Subscribes to OSU map updates and stores versions for later review.
+
+Please don't run a separate bot, the official one is `subscribe-bot#8789`. If
+you want to contribute or test the bot, then here are instructions on how to
+run it:
+
+How to run
+----------
+
+1. Build the bot using a Go compiler that supports modules (1.11 or higher).
+   Running `go build` in the root of the repo should work.
+1. Create a configuration file called `config.toml` (can be called something
+   else as long as you pass it into the executable as a command-line argument).
+    - `client_id` (int) and `client_secret` (string) are oauth-related settings
+    you can obtain from the OSU settings page.
+    - `bot_token` (string) is Discord's bot auth{entication,orization} token,
+    you can get that from Discord developers' page.
+    - `repos` (path) is a path to where map repositories should be stored.
+1. Run the executable, passing `-config {path}` in case you want to use a
+   different config file than `config.toml`.
+
+License
+-------
+
+[GPL3][1]
+
+[1]: https://www.gnu.org/licenses/gpl-3.0.en.html