improve installation instructions

docs/installation_instructions.md

@@ -95,8 +95,10 @@ There are two options to create a cluster:
     3. Click "API keys"
     4. Click "New API key"
     5. Click "Generate new key"
-    6. Give the key "Customer", "CloudCustomer" or "API" access rights (this
-       depends on what righs your user has. Any of these three is fine)
+    6. Give the key "Customer", "CloudCustomer" or "API" access rights. You'll
+       need "Customer" rights if you want to automatically generate DNS rules.
+       If you don't have this right, you have to manually set the right DNS
+       rules.
     7. Copy the generated key and run export it to this variable in a terminal:
 
        ```
@@ -136,7 +138,7 @@ There are two options to create a cluster:
   - Here's an example of the complete creation command: 
 
     ```
-    python3 -m openappstack my-cluster create --create-droplet --hostname oas.example.org --ssh-key-id 112 --create-domain-records --subdomain oas example.org
+    python -m openappstack my-cluster create --create-droplet --hostname oas.example.org --ssh-key-id 112 --create-domain-records --subdomain oas example.org
     ```
 
     This will create configuration files for a cluster named `my-cluster. It