Change wrong number in nx-cloud docs which determine number of agents
for small changes which is 3 not 1
The workflow is:
```yaml
distribute-on:
small-changeset: 3 linux-medium-js
medium-changeset: 6 linux-medium-js
large-changeset: 10 linux-medium-js
```
but docs says:
`Now PRs that affect a small percentage of the repo will run on 1 agent,
.....`
Which is not matching the workflow and it should be 3 not 1
https://nx.dev/ci/features/dynamic-agents#dynamically-allocate-agents
