Add note on rules for scraping pods (#358)

Added clarifying rules from #316 (comment) for the default script config to scrape pods.

docs/getting-started.md

@@ -64,6 +64,12 @@ NAMESPACE="default" /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com
 NAMESPACE="default" /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/grafana/agent/release/production/kubernetes/install-loki.sh)" | kubectl apply -f -
 NAMESPACE="default" /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/grafana/agent/release/production/kubernetes/install-tempo.sh)" | kubectl apply -f -
 ```
+**Note:** For the above script to scrape your pods, they must conform to the following rules:
+
+1. The pod must _not_ have an annotation matching `prometheus.io/scrape: "false"` (this wouldn't be there unless you explicitly add it or if you deploy a Helm chart that has it).
+2. The pod _must_ have a port with a name ending in `-metrics`. This is the port that will be scraped by the Agent. A lot of people using Helm struggle with this, since Helm charts don't usually follow this. You would need to add a new scrape config to scrape helm charts or find a way to tweak the Helm chart to follow this rules.
+3. The pod _must_ have a label named name with any non-empty value. Helm usually lets you add extra labels, so this is less of a problem for Helm users.
+4. The pod must currently be running. (i.e., Kubernetes must not report it having a phase of Succeeded or Failed).
 
 ### Kubernetes Manifest