Add a readme (#4)

README.md

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+# rules_graal
+
+Turn a JVM binary into a native binary.
+
+## Usage
+
+You'll need to first load the rules in your WORKSPACE file.
+
+``` python
+git_repository(
+    name = "rules_graal",
+    commit = "<<pick-a-recent-commit-sha>>",
+    remote = "git://github.com/andyscott/rules_graal",
+)
+
+load("//graal:graal_bindist.bzl", "graal_bindist_repository")
+
+graal_bindist_repository(
+    name = "graal",
+    version = "1.0.0-rc16",
+)
+```
+
+Then, in a build file:
+
+```python
+load("@rules_graal//graal:graal.bzl", "graal_binary")
+
+java_library(
+    name = "main",
+    srcs = glob(["Main.java"]),
+)
+
+graal_binary(
+    name = "main-native",
+    deps = [":main"],
+    main_class = "Main",
+)
+```