Refactor installtion docs

docs/installation/2-redis.md

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+[Redis](https://redis.io/) is an in-memory key-value store which NetBox employs for caching and queuing. This section entails the installation and configuration of a local Redis instance. If you already have a Redis service in place, skip to [the next section](3-netbox.md).
+
+#### Ubuntu
+
+```no-highlight
+# apt-get install -y redis-server
+```
+
+#### CentOS
+
+```no-highlight
+# yum install -y redis
+```
+
+## Verify Service Status
+
+Use the `redis-cli` utility to ensure the Redis service is functional:
+
+```no-highlight
+$ redis-cli ping
+PONG
+```