docs: add build step to docs (#1275)

Now that we need to build ts to js a build step is necessary.

Add it to the instructions where we are telling people to clone the repo first.

Refs: #1273

examples/libp2p-in-the-browser/README.md

@@ -6,11 +6,12 @@ This example leverages the [Parcel.js bundler](https://parceljs.org/) to compile
 
 In order to run the example:
 
-- Install dependencey at the root of the js-libp2p repository (if not already done), 
+- Install dependencey at the root of the js-libp2p repository (if not already done),
 - then, install the dependencies from same directory as this README:
 
 ```
 npm install
+npm run build
 cd ./examples/libp2p-in-the-browser
 npm install
 ```