feat: 适配路由器的内存指标

[nangongchengfeng]

您好，目前我使用这个组件监控路由器指标，目前再次基础上增加内存指标监控。
PR:

• 增加内存监控的四个指标
• 增加一些注释
• 增加首页跳转指标页面

node_memory_buffers_bytes 0
# HELP node_memory_cached_bytes Cached memory in bytes.
# TYPE node_memory_cached_bytes gauge
node_memory_cached_bytes 1.1230531584e+10
# HELP node_memory_free_bytes Free memory in bytes.
# TYPE node_memory_free_bytes gauge
node_memory_free_bytes 3.25373952e+08
# HELP node_memory_total_bytes Total memory in bytes.
# TYPE node_memory_total_bytes gauge
node_memory_total_bytes 3.356504064e+10

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[Bpazy]

nice pr, 非常感谢

[Bpazy]

PR release at v0.3.0: https://github.com/Bpazy/padavan_exporter/releases/tag/v0.3.0