[user-guide] Inject node description improvement and related links

Context

• Guide URL: https://nodered.org/docs/user-guide/nodes
• Source URL: https://github.com/node-red/node-red.github.io/blob/master/docs/user-guide/nodes.md
• Section: Inject node
• Text snippet:

If you are looking at intervals greater than one day - consider using a scheduler node that can cope with power outages and restarts.

Problem or Improvement

In this section, it is said: ...consider using a scheduler node....

This is mostly unclear for the newcomer who reads the guide, as:

1. There is no scheduler core node type.
2. There is no reference or link to no-core nodes which fulfill such task, so the user can further research that option if needed.

Suggestion

Update the node description to tackle on this unclear reference.

打开 docs/user-guide/nodes.md 并找到 Inject node 部分。检查当前关于 scheduler 的措辞，并添加说明以及指向能够处理断电和重启期间调度的 no-core nodes 的相关链接；该指南不应再暗示存在 core scheduler node。