create readme in examples directory

Author: nonnontrivial

examples/README.md

@@ -0,0 +1,23 @@
+# `async-std` Examples
+
+This directory contains example code that makes use of `async-std`.
+
+Each example can be run from the command line.
+
+For example, [Hello World][hello-world] can be run by running the following:
+
+```
+cargo run --example hello-world
+```
+
+- [Hello World][hello-world]
+
+Spawns a task that says hello.
+
+- [Line Count][line-count]
+
+Counts the number of lines in a file given as an argument.
+
+[hello-world]: https://github.com/async-rs/async-std/blob/master/examples/hello-world.rs
+[line-count]: https://github.com/async-rs/async-std/blob/master/examples/line-count.rs
+<!-- [list-dir]: https://github.com/async-rs/async-std/blob/master/examples/list-dir.rs -->