[docs]: Understanding how merge rules work

# Documentation request

https://cloudinit.readthedocs.io/en/latest/reference/merging.html#specifying-multiple-types-and-what-this-does

Hello,

I'm trying to understand how merging rules behave, since I'm getting a different behavior than my interpretation of the documentation.

I have a simple case, where, I'm using a `#cloud-config-archive` with two `#cloud-config` parts. Let's call them CC1 (cloud-config 1) and CC2 (cloud-config 2).

```
#cloud-config-archive
- type: 'text/cloud-config'
content: |
#cloud-config
merge_how:
- name: list
settings: ['append']
- name: list
settings: ['no_replace', 'recurse_list']
runcmd:
- echo "Hello, World!" > /tmp/hello.txt

- type: 'text/cloud-config'
content: |
#cloud-config
runcmd:
- echo "Hello, World! 2" > /tmp/hello2.txt
```

Based on the documentation, my interpretation is that, after CC1 is processed, `merge_how` rules will apply to CC2 gets merged into CC1. That doesn't seem to be happening. Now, if I move the `merge_how` rules to CC2, I get the expected behavior where runcmd has both commands.

I just want to understand if I'm misunderstanding the documentation and there might be an opportunity for improvement.

Thanks