[PSDK-187] Server Signer Support (#42)

* [PSDK-187] Server Signer Support

* tests

* use configuration option types for constructors

* typedocs

* nits

* readme

* pr review

* update docs

* update typedocs

README.md

@@ -77,15 +77,20 @@ To start, [create a CDP API Key](https://portal.cdp.coinbase.com/access/api). Th
 ```typescript
 const apiKeyName = "Copy your API Key name here.";
 
-const apiKeyPrivateKey = "Copy your API Key's private key here.";
+const privatekey = "Copy your API Key's private key here.";
 
-const coinbase = new Coinbase(apiKeyName, apiKeyPrivateKey);
+const coinbase = new Coinbase({ apiKeyName: apiKeyName, privateKey: privateKey });
+```
+
+If you are using a CDP Server-Signer to manage your private keys, enable it with the constuctor option:
+```typescript
+const coinbase = new Coinbase({ apiKeyName: apiKeyName, privateKey: apiKeyPrivateKey, useServerSigner: true })
 ```
 
 Another way to initialize the SDK is by sourcing the API key from the json file that contains your API key, downloaded from CDP portal.
 
 ```typescript
-const coinbase = Coinbase.configureFromJson("path/to/your/api-key.json");
+const coinbase = Coinbase.configureFromJson({ filePath: "path/to/your/api-key.json" });
 ```
 
 This will allow you to authenticate with the Platform APIs and get access to the default `User`.