Add installer example

README.md

@@ -1,4 +1,4 @@
-# Web Authentication for PHP
+# Web Authentication (Passkeys) for PHP
 
 A way to move beyond passwords
 
@@ -25,6 +25,12 @@ Application logic is kept to a bare minimum in order to highlight the most impor
 
 ### Setup
 
+First, install the library:
+
+```
+composer require firehed/webauthn
+```
+
 Create a `RelyingParty` instance.
 This **MUST** match the complete origin that users will interact with; e.g. `https://login.example.com:1337`.
 The protocol is always required; the port must only be present if using a non-standard port and must be excluded for standard ports.