Fix minor issues pointed out in the review

crates/plugin_runtime/README.md

@@ -31,6 +31,7 @@ All functions that Plugin exports must have the following properties:
 Additionally, Plugin must export an:
 
 - `__alloc_buffer` function that, given a `u32` length, returns a `u32` pointer to a buffer of that length.
+- `__free_buffer` function that, given a buffer encoded as a `u64`, frees the buffer at the given location, and does not return anything.
 
 Note that all of these requirements are automatically fullfilled for any Rust Wasm plugin that uses the `plugin` crate, and imports the `prelude`. 
 

crates/plugin_runtime/build.rs

@@ -4,8 +4,8 @@ use wasmtime::{Config, Engine};
 fn main() {
     let base = Path::new("../../plugins");
 
-    // println!("cargo:rerun-if-changed=../../plugins/*");
-    println!("cargo:warning=Precompiling plugins...");
+    println!("cargo:rerun-if-changed={}", base.display());
+    println!("cargo:warning=Rebuilding precompiled plugins...");
 
     let _ = std::fs::remove_dir_all(base.join("bin"));
     let _ =

crates/plugin_runtime/src/plugin.rs

@@ -16,7 +16,9 @@ use wasmtime_wasi::{Dir, WasiCtx, WasiCtxBuilder};
 /// Represents a resource currently managed by the plugin, like a file descriptor.
 pub struct PluginResource(u32);
 
-#[repr(C)]
+/// This is the buffer that is used Host side.
+/// Note that it mirrors the functionality of
+/// the `__Buffer` found in the `plugin/src/lib.rs` prelude.
 struct WasiBuffer {
     ptr: u32,
     len: u32,