Reflect NPM package in README
The README was still referencing the outdated GitHub Package Registry
deployment.
@@ -31,22 +31,21 @@ https://discord.gg/4R6RGFf[Discord].
== Installation
-tBTC contracts are currently published in the GitHub Package Registry.
+tBTC contracts are currently published in the NPM Registry as the package
+[`@keep-network/tbtc`](https://www.npmjs.com/package/@keep-network/tbtc).
+Packages have versions corresponding to their network:
-1. Add a file `.npmrc` to the same directory as your project's
-`package.json`.
-2. Paste the following to configure the GitHub Package Registry for
-tBTC:
-+
-....
-@keep-network:registry=https://npm.pkg.github.com/keep-network
-....
-3. Install the package:
-+
-[source,sh]
-----
+- `-pre` packages contain prerelease packages for the internal Keep testnet.
+- `-rc` packages contain prerelease packages for the Ropsten Ethereum testnet.
+
+Note that only the latest package in a series is expected to reference
+contracts that have a backing set of signers.
+
+To install the package:
+
+```sh
$ npm install @keep-network/tbtc
-----
+```
== Usage
