Move miscellaneous tidbits from README to miscellaneous.md and other files

docs/user-guide/customizing-nginx.md

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+# Customizing NGINX
+
+There are three ways to customize NGINX:
+
+1. [ConfigMap](./configmap.md): using a Configmap to set global configurations in NGINX.
+2. [Annotations](./annotations.md): use this if you want a specific configuration for a particular Ingress rule.
+3. [Custom template](./custom-template.md): when more specific settings are required, like [open_file_cache](http://nginx.org/en/./http/ngx_http_core_module.html#open_file_cache), adjust [listen](http://nginx.org/en/./http/ngx_http_core_module.html#listen) options as `rcvbuf` or when is not possible to change the configuration through the ConfigMap.

docs/user-guide/multiple-ingress.md

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+# Multiple ingress controllers
+
+## Running multiple ingress controllers
+
+If you're running multiple ingress controllers, or running on a cloud provider that natively handles ingress, you need to specify the annotation `kubernetes.io/ingress.class: "nginx"` in all ingresses that you would like this controller to claim.  This mechanism also provides users the ability to run _multiple_ NGINX ingress controllers (e.g. one which serves public traffic, one which serves "internal" traffic).  When utilizing this functionality the option `--ingress-class` should be changed to a value unique for the cluster within the definition of the replication controller. Here is a partial example:
+
+```
+spec:
+  template:
+     spec:
+       containers:
+         - name: nginx-ingress-internal-controller
+           args:
+             - /nginx-ingress-controller
+             - '--default-backend-service=ingress/nginx-ingress-default-backend'
+             - '--election-id=ingress-controller-leader-internal'
+             - '--ingress-class=nginx-internal'
+             - '--configmap=ingress/nginx-ingress-internal-controller'
+```
+
+
+## Annotation ingress.class
+
+If you have multiple Ingress controllers in a single cluster, you can pick one by specifying the `ingress.class` 
+annotation, eg creating an Ingress with an annotation like
+
+```yaml
+metadata:
+  name: foo
+  annotations:
+    kubernetes.io/ingress.class: "gce"
+```
+
+will target the GCE controller, forcing the nginx controller to ignore it, while an annotation like
+
+```yaml
+metadata:
+  name: foo
+  annotations:
+    kubernetes.io/ingress.class: "nginx"
+```
+
+will target the nginx controller, forcing the GCE controller to ignore it.
+
+__Note__: Deploying multiple ingress controller and not specifying the annotation will result in both controllers fighting to satisfy the Ingress.
+
+## Disabling NGINX ingress controller
+
+Setting the annotation `kubernetes.io/ingress.class` to any other value  which does not match a valid ingress class will force the NGINX Ingress controller to ignore your Ingress.  If you are only running a single NGINX ingress controller, this can be achieved by setting this to any value except "nginx" or an empty string.
+
+Do this if you wish to use one of the other Ingress controllers at the same time as the NGINX controller.
+