Add comprehensive documentation comments

options.go

@@ -5,20 +5,49 @@ import (
 	"time"
 )
 
+// Option is a function type that modifies a Client during initialization.
+// Options follow the functional options pattern for configuring client behavior.
 type Option func(*Client)
 
+// WithBaseURL returns an Option that sets a custom API base URL for the client.
+// Use this to point to a different Sendamatic API endpoint or a testing environment.
+//
+// Example:
+//
+//	client := sendamatic.NewClient("user", "pass",
+//		sendamatic.WithBaseURL("https://custom.api.url"))
 func WithBaseURL(baseURL string) Option {
 	return func(c *Client) {
 		c.baseURL = baseURL
 	}
 }
 
+// WithHTTPClient returns an Option that replaces the default HTTP client with a custom one.
+// This allows full control over HTTP behavior such as transport settings, connection pooling,
+// and custom middleware.
+//
+// Example:
+//
+//	customClient := &http.Client{
+//		Timeout: 60 * time.Second,
+//		Transport: customTransport,
+//	}
+//	client := sendamatic.NewClient("user", "pass",
+//		sendamatic.WithHTTPClient(customClient))
 func WithHTTPClient(client *http.Client) Option {
 	return func(c *Client) {
 		c.httpClient = client
 	}
 }
 
+// WithTimeout returns an Option that sets the HTTP client timeout duration.
+// This determines how long the client will wait for a response before timing out.
+// The default timeout is 30 seconds.
+//
+// Example:
+//
+//	client := sendamatic.NewClient("user", "pass",
+//		sendamatic.WithTimeout(60*time.Second))
 func WithTimeout(timeout time.Duration) Option {
 	return func(c *Client) {
 		c.httpClient.Timeout = timeout