docs/customizations: Move customization examples to dedicated folder

With the objective of improving our README, customization examples are being moved to a dedicated folder under `docs/`.

Signed-off-by: ArthurSens <arthursens2005@gmail.com>

docs/customizations/platform-specific.md

@@ -0,0 +1,25 @@
+### Running kube-prometheus on specific platforms
+
+A common example is that not all Kubernetes clusters are created exactly the same way, meaning the configuration to monitor them may be slightly different. For the following clusters there are mixins available to easily configure them:
+
+* aws
+* bootkube
+* eks
+* gke
+* kops
+* kops_coredns
+* kubeadm
+* kubespray
+
+These mixins are selectable via the `platform` field of kubePrometheus:
+
+```jsonnet mdox-exec="cat examples/jsonnet-snippets/platform.jsonnet"
+(import 'kube-prometheus/main.libsonnet') +
+{
+  values+:: {
+    common+: {
+      platform: 'example-platform',
+    },
+  },
+}
+```