docs: link fixes (#80)

Author: vonovak

docs/buttons/web.mdx

@@ -13,7 +13,7 @@ import Banner from '../_sponsorBanner.mdx';
 
 The button will _not render_ before the [Google Client API has been loaded](../setting-up/web). You can use the `onError` prop to detect this case.
 
-### How to use this
+### Usage
 
 As the Universal sign in Guide explains, there are two ways to sign in on the web: using the One-tap UI or using the Google Sign-In button.
 

docs/security.mdx

@@ -90,7 +90,7 @@ export const getNonce = async () => {
   // Supabase makes a hash of `rawNonce` and compares it with the `nonceDigest`
   // which is included in the ID token from RN-google-signin.
   const rawNonce = getUrlSafeNonce();
-  // `nonceDigest` goes to the `nonce` parameter in RN-google-signin APIs
+  // `nonceDigest` (SHA-256 hash, hex-encoded) goes to the `nonce` parameter in RN-google-signin APIs
   const nonceDigest = await digestStringAsync(
     CryptoDigestAlgorithm.SHA256,
     rawNonce,

docs/setting-up/expo.md

@@ -22,7 +22,7 @@ After installing the npm package, add a config plugin (read more details below)
 
 If you're _not_ using Firebase, provide the `iosUrlScheme` option to the config plugin.
 
-To obtain `iosUrlScheme`, follow [the guide](./get-config-file#ios).
+To obtain `iosUrlScheme`, follow [the guide](./get-config-file?firebase-or-not=cloud-console#ios).
 
 ```json title="app.json | js"
 {
@@ -41,7 +41,7 @@ To obtain `iosUrlScheme`, follow [the guide](./get-config-file#ios).
 
 ### Expo and Firebase Authentication
 
-If you are using Firebase Authentication, obtain the 2 Firebase config files (`google-services.json` for Android and `GoogleService-Info.plist` for iOS) according to the [guide](./get-config-file?firebase-or-not=firebase) and place them into your project. Then specify the paths to the files:
+If you are using Firebase Authentication, obtain the 2 Firebase config files (`google-services.json` for Android and `GoogleService-Info.plist` for iOS) according to the [guide](./get-config-file?firebase-or-not=firebase#ios) and place them into your project. Then specify the paths to the files:
 
 ```json title="app.json | js"
 {