Add doc for acquiring Azure Client Id.

docs/MicrosoftAuth.md

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+# Microsoft Authentication
+
+Authenticating with Microsoft is fully supported by Helios Launcher.
+
+## Acquiring an Azure Client ID
+
+1. Navigate to https://portal.azure.com
+2. In the search bar, search for **Azure Active Directory**.
+3. In Azure Active Directory, go to **App Registrations** on the left pane (Under *Manage*).
+4. Click **New Registration**.
+    - Set **Name** to be your launcher's name.
+    - Set **Supported account types** to *Accounts in any organizational directory (Any Azure AD directory - Multitenant) and personal Microsoft accounts (e.g. Skype, Xbox)*
+    - Leave **Redirect URI** blank.
+    - Register the application.
+5. You should be on the application's management page. If not, Navigate back to **App Registrations**. Select the application you just registered.
+6. Click **Authentication** on the left pane (Under *Manage*).
+7. Click **Add Platform**.
+    - Select **Mobile and desktop applications**.
+    - Choose `https://login.microsoftonline.com/common/oauth2/nativeclient` as the **Redirect URI**.
+    - Select **Configure** to finish adding the platform.
+8. Navigate back to **Overview**.
+9. Copy **Application (client) ID**.
+
+
+Reference: https://docs.microsoft.com/en-us/azure/active-directory/develop/quickstart-register-app
+
+## Adding the Azure Client ID to Helios Launcher.
+
+In `app/assets/js/ipcconstants.js` you'll find **`AZURE_CLIENT_ID`**, replace `FILL-IN` with your application's id.
+
+Note: Azure Client ID is NOT a secret value and **can** be stored in git. Reference: https://stackoverflow.com/questions/57306964/are-azure-active-directorys-tenantid-and-clientid-considered-secrets
+
+----
+
+You can now authenticate with Microsoft through the launcher.