Update usage.md (#306)

Author: mjgp2

docs/usage.md

@@ -225,7 +225,7 @@ expose(counter)
 
 You can spawn `*.ts` workers out-of-the-box without prior transpiling if <a href="https://github.com/TypeStrong/ts-node" rel="nofollow">ts-node</a> is installed.
 
-If the path passed to `new Worker()` resolves to a `*.ts` file, threads.js will check if `ts-node` is available. If so, it will create an in-memory module that wraps the actual worker module and initializes `ts-node` before running the worker code.
+If the path passed to `new Worker()` resolves to a `*.ts` file, threads.js will check if `ts-node` is available. If so, it will create an in-memory module that wraps the actual worker module and initializes `ts-node` before running the worker code. *It is likely you will have to increase the THREADS_WORKER_INIT_TIMEOUT environment variable (milliseconds, default 10000) to account for the longer ts-node startup time if you see timeouts spawning threads.*
 
 In case `ts-node` is not available, `new Worker()` will attempt to load the same file, but with a `*.js` extension. It is then in your hands to transpile the worker module before running the code.