chore: implement create label from rate docs (#20)

* implement create label from rate docs

* title update

Author: j-r-j

docs/create-label-from-rate.md

@@ -1,5 +1,111 @@
 Create Label From Rate
 ======================================
-When retrieving rates for shipments using the `getRates` method, the returned information contains a `rate_id` property that can be used to purchase a label without having to refill in the shipment information repeatedly.
+[ShipEngine](www.shipengine.com) allows you programmatically create shipping labels. You can use the `create_label_from_rate` to create a shipping label from pre defined shipment information that is persisted in the `rate_id` that is passed to the function. Please see [our docs](https://www.shipengine.com/docs/labels/create-from-rate/) to learn more about creating shipping labels from a rate.
 
-> Coming Soon
+Input Parameters
+-------------------------------------
+
+The `create_label_from_rate` method requires a `rate_id` as well as some label details that are detailed in the documentation above.
+
+Output
+--------------------------------
+The `create_label_from_rate` method returns the label that was created in a response class of ShipEngine::Domain::Labels::CreateFromRate::Response.
+
+Example
+```ruby
+def create_label_from_rate_demo_function()
+	client = ShipEngine::Client.new("API-Key")
+
+	params = {
+	  validate_address: "no_validation",
+	  label_layout: "4x6",
+	  label_format: "pdf",
+	  label_download_type: "url",
+	  display_scheme: "label"
+	}
+
+	begin
+	  result = client.create_label_from_rate('se-795684260', params)
+		puts result
+	rescue ShipEngine::Exceptions::ShipEngineError => err
+	  puts err
+	end
+end
+
+create_label_from_rate_demo_function
+```
+
+Example Output
+-----------------------------------------------------
+
+### Successful Create Label From Rate Result
+```ruby
+#<ShipEngine::Domain::Labels::CreateFromRate::Response
+ @batch_id="",
+ @carrier_code="stamps_com",
+ @carrier_id="se-423887",
+ @charge_event="carrier_default",
+ @created_at="2021-08-03T19:52:40.6378591Z",
+ @display_scheme="label",
+ @form_download=nil,
+ @insurance_claim=nil,
+ @insurance_cost=
+  #<ShipEngine::Domain::Labels::CreateFromRate::Response::MonetaryValue
+   @amount=0.0,
+   @currency="usd">,
+ @is_international=false,
+ @is_return_label=false,
+ @label_download=
+  #<ShipEngine::Domain::Labels::CreateFromRate::Response::LabelDownload
+   @href=
+    "https://api.shipengine.com/v1/downloads/10/nqQR0gqdkUmd_UWNiRy6Ew/label-75301494.pdf",
+   @pdf=
+    "https://api.shipengine.com/v1/downloads/10/nqQR0gqdkUmd_UWNiRy6Ew/label-75301494.pdf",
+   @png=
+    "https://api.shipengine.com/v1/downloads/10/nqQR0gqdkUmd_UWNiRy6Ew/label-75301494.png",
+   @zpl=
+    "https://api.shipengine.com/v1/downloads/10/nqQR0gqdkUmd_UWNiRy6Ew/label-75301494.zpl">,
+ @label_format="pdf",
+ @label_id="se-75301494",
+ @label_image_id=nil,
+ @label_layout="4x6",
+ @package_code="package",
+ @packages=
+  [#<ShipEngine::Domain::Labels::CreateFromRate::Response::Package
+    @dimensions=
+     #<ShipEngine::Domain::Labels::CreateFromRate::Response::Dimensions
+      @height=0.0,
+      @length=0.0,
+      @unit="inch",
+      @width=0.0>,
+    @external_package_id=nil,
+    @insured_value=
+     #<ShipEngine::Domain::Labels::CreateFromRate::Response::MonetaryValue
+      @amount=0.0,
+      @currency="usd">,
+    @label_messages=
+     #<ShipEngine::Domain::Labels::CreateFromRate::Response::Package::LabelMessages
+      @reference1=nil,
+      @reference2=nil,
+      @reference3=nil>,
+    @package_code="package",
+    @tracking_number="9400111899560334170636",
+    @weight=
+     #<ShipEngine::Domain::Labels::CreateFromRate::Response::Weight
+      @unit="ounce",
+      @value=1.0>>],
+ @rma_number=nil,
+ @service_code="usps_first_class_mail",
+ @ship_date="2021-08-03T00:00:00Z",
+ @shipment_cost=
+  #<ShipEngine::Domain::Labels::CreateFromRate::Response::MonetaryValue
+   @amount=3.35,
+   @currency="usd">,
+ @shipment_id="se-144039990",
+ @status="completed",
+ @trackable=true,
+ @tracking_number="9400111899560334170636",
+ @tracking_status="in_transit",
+ @voided=false,
+ @voided_at=nil>
+```