Added Frequently Asked Questions page (#65)

* Added initial FAQ page

* Added TOC entry for the FAQ

FAQ.md

@@ -0,0 +1,27 @@
+# Frequently Asked Questions
+
+Below are a number of questions or issues that have arisen from using the SDK.
+
+## Why does the `Auth0Client` object take a long time to initialize?
+
+Sometimes the `createAuth0Client` asynchronous method can take over 30 seconds to complete. This is usually down to a configuration problem between your application, and the Auth0 application you're trying to log in with. Things to check:
+
+- Make sure that options passed to `createAuth0Client` include the correct client ID and domain values for the app you're using
+- Ensure that the **Allowed Callback URLs**, **Allowed Web Origins**, and **Allowed Logout URLs** are [correctly set up in your Auth0 app settings](https://auth0.com/docs/quickstart/spa/react/#configure-callback-urls) for your application
+
+To verify that you're hitting this problem, [check the logs](https://manage.auth0.com/#/logs) in your Auth0 dashboard for any failed login events, which may provide a clue as to the problem.
+
+## Why do I get an "invalid algorithm" error?
+
+The SDK only supports JWTs that use the **RS256** [signing algorithm](https://auth0.com/docs/applications/concepts/signing-algorithms). If you're getting this error, it's likely that the Auth0 application you're authenticating with is set up to sign tokens using **HS256**.
+
+The way around this error is to change the settings for your Auth0 application to sign tokens using RS256. To do this:
+
+- Log in to [your dashboard](https://manage.auth0.com)
+- Open the settings page for the application you're using
+- Scroll to the bottom and click **Show advanced settings**
+- Click the **OAuth** tab
+- Ensure the **JsonWebToken Signature Algorithm** value is set to **RS256**
+- Click **Save**
+
+The next time you try to authenticate, you should not receive this error.

README.md

@@ -14,6 +14,7 @@ Make sure this is updated based on the sections included:
 - [Getting Started](#getting-started)
 - [Contributing](#contributing)
 - [Support + Feedback](#support--feedback)
+- [Frequently Asked Questions](#frequently-asked-questions)
 - [Vulnerability Reporting](#vulnerability-reporting)
 - [What is Auth0](#what-is-auth0)
 - [License](#license)
@@ -158,6 +159,10 @@ This SDK is in Early Access with selected stakeholders.
 
 We process feedback and provide support via private channels.
 
+## Frequently Asked Questions
+
+For a rundown of common issues you might encounter when using the SDK, please check out [the FAQ](FAQ.md).
+
 ## Vulnerability Reporting
 
 Please do not report security vulnerabilities on the public GitHub issue tracker. The [Responsible Disclosure Program](https://auth0.com/whitehat) details the procedure for disclosing security issues.