chore: improve client explanation guide

guides/explanations/0.client.md

@@ -6,6 +6,47 @@ and responses—such as adding headers or handling authentication—while adapte
 handle the underlying HTTP communication. For more details, see the sections on
 [middleware](./2.middleware.md) and [adapters](./3.adapter.md).
 
+## Creating a Client
+
+A client is created using `Tesla.client/2`, which takes a list of middleware
+and an adapter.
+
+```elixir
+client = Tesla.client([Tesla.Middleware.PathParams, Tesla.Middleware.Logger])
+```
+
+You can then use the client to make requests:
+
+```elixir
+Tesla.get(client, "/users/123")
+```
+
+### Passing Options to Middleware
+
+You can pass options to middleware by registering the middleware as a tuple
+of two elements, where the first element is the middleware module and the
+second is the options.
+
+```elixir
+client = Tesla.client(
+  [{Tesla.Middleware.BaseUrl, "https://api.example.com"}]
+)
+```
+
+### Passing Adapter
+
+By default, the global adapter is used. You can override this by passing an
+adapter to the client.
+
+```elixir
+client = Tesla.client([], Tesla.Adapter.Mint)
+```
+You can also pass options to the adapter.
+
+```elixir
+client = Tesla.client([], {Tesla.Adapter.Mint, pool: :my_pool})
+```
+
 ## Single-Client (Singleton) Pattern
 
 A common approach in applications is to encapsulate client creation within a