docs: add apikey.yml example and explanation

.gitignore

@@ -1,3 +1,5 @@
 .venv
 **/__pycache__
+
 apikey.yml
+domains.json

README.md

@@ -13,8 +13,8 @@ Python libraries:
 Install the [dependencies](#dependencies), preferrably using your system's package manager.
 
 Next, you will need your Ionos API keypair.
-Clone the repo and create a file called `apikey.yml` at the project root.
-Inside the file, paste your Ionos API-keypair in the following format:
+Clone the repo and edit the file `apikey.yml`.
+Inside the file, paste the respective value of your Ionos API-keypair, following this format:
 
 ```yaml
 ---
@@ -26,6 +26,8 @@ apikey:
 ...
 ```
 
+This file **must be kept secret**.
+
 ### Adding target domains
 
 Add every domain you want to send an update for to the file `domains.json`.

apikey.yml

@@ -0,0 +1,7 @@
+---
+
+apikey:
+  prefix: <your api key prefix>
+  secret: <your api key secret>
+
+...