Update README.md
Document that Java 11 is needed to build the compiler.
@@ -213,7 +213,7 @@ To build the compiler yourself, you will need the following:
Prerequisite | Description
-------------------------------------------------------------------------- | -----------
-[Java 8 or later](https://java.com) | Used to compile the compiler's source code.
+[Java 11 or later](https://java.com) | Used to compile the compiler's source code.
[Git](https://git-scm.com/) | Used by Bazel to download dependencies.
[Bazelisk](https://bazel.build/install/bazelisk) | Used to build the various compiler targets.
