example code

[keredson]

this could use an example for non-async, non-std.

i had to patch in a custom getrandom impl to use:

        #[path = "espidf.rs"] mod imp;

for some reason if #[cfg(target_os = "espidf")] wasn't true. this was in a new cargo generate esp-rs/esp-template.

beyond that, re the async example, depending on sunset-async seems to pull in stuff that depends on std. example:

error[E0463]: can't find crate for `alloc`
  --> /home/derek/.cargo/registry/src/index.crates.io-6f17d22bba15001f/futures-core-0.3.30/src/lib.rs:16:1
   |
16 | extern crate alloc;
   | ^^^^^^^^^^^^^^^^^^^ can't find crate