Add cross-links to Zulip, etc.

README.md

@@ -1,8 +1,13 @@
 # stdsimd - Rust's standard library portable SIMD API
-
 [![Build Status](https://travis-ci.com/rust-lang/stdsimd.svg?branch=master)](https://travis-ci.com/rust-lang/stdsimd)
 
 Code repository for the [Portable SIMD Project Group](https://github.com/rust-lang/project-portable-simd).
+Please refer to [CONTRIBUTING.md](./CONTRIBUTING.md) for our contributing guidelines.
+
+If you have questions about SIMD, we have begun writing a [guide][simd-guide].
+We can also be found on [Zulip][zulip-project-portable-simd].
+
+If you are interested in support for a specific architecture, you may want [stdarch] instead.
 
 ## Code Organization
 
@@ -20,3 +25,7 @@ The supported element types are as follows:
 
 Floating point, signed integers, and unsigned integers are the [primitive types](https://doc.rust-lang.org/core/primitive/index.html) you're already used to.
 The `mask` types are "truthy" values, but they use the number of bits in their name instead of just 1 bit like a normal `bool` uses.
+
+[simd-guide]: ./beginners-guide.md
+[zulip-project-portable-simd]: https://rust-lang.zulipchat.com/#narrow/stream/257879-project-portable-simd
+[stdarch]: https://github.com/rust-lang/stdarch