Readme update

Author: MrZoidberg

README.md

@@ -11,9 +11,51 @@ VaultSharp.Extensions.Configuration can be installed using the Nuget package man
 `dotnet add package VaultSharp.Extensions.Configuration`
 
 It can be injected as a [IConfigurationProvider](https://docs.microsoft.com/en-us/dotnet/api/microsoft.extensions.configuration.iconfigurationprovider?view=dotnet-plat-ext-3.1)
-to load configuration from HashiCorp Vault.
+to load configuration from HashiCorp Vault:
 
+```csharp
+public static IHostBuilder CreateHostBuilder(string[] args) =>
+    Host.CreateDefaultBuilder(args)
+        .ConfigureAppConfiguration((hostingContext, config) =>
+        {
+            config.AddJsonFile("appsettings.json")
+                .AddVaultConfiguration(() => new VaultOptions("http://localhost:8200", "root"), "sampleapp", "secret");
+        })
+        .ConfigureWebHostDefaults(webBuilder =>
+        {
+            webBuilder.UseStartup<Startup>();
+        });
+```
 
+The `AddVaultConfiguration` method accepts several parameters:
+
+1. Function to provide VaultOptions with Vault connection configuration (optional).
+
+2. Application alias in Vault data. It's used a part of the path to read secrets.
+
+3. Mount point of KV secrets. The default value is `secret` (optional).
+
+## Configuration using environmnt variables
+
+Alternatively, you can configure Vault connection using next environmnt variables:
+
+- `VAULT_ADDR` : Address of the Vault instance. Default value is `"http://locahost:8200`.
+- `VAULT_TOKEN` : Vault token. Used for token-based authentication. Default value is `root`.
+- `VAULT_ROLEID` : Vault AppRole ID. Used for AppRole-based authentication.
+- `VAULT_SECRET` : Vault AppRole secret. Used for AppRole-based authentication.
+
+## Preparing secrets in Vault
+
+You need to store your secrets with special naming rules.
+First of all, all secrets should use KV2 storage and have prefix `data/{app_alias}/`.
+For example, if your app has alias `sampleapp` and you want to have configuration option `ConnectionString` your secret path would be `data/sampleapp/ConnectionString`.
+
+All secret data should use JSON format with the only key `value` and secret data inside:
+```json
+{
+    "value": "secret value"
+}
+```
 
 ## Limitations