Add documentation.

Author: style95

docs/dedicated-invokers.md

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+
+# Dedicated Invokers
+
+Actions run on any invokers in OpenWhisk. But users may want to run their actions on a certain invoker(s) for some reason such as IP-based ACL.
+This is to provide dedicated invokers for a namespace. Operators can configure a dedicated namespace for invokers and all activations from the namespace will be delivered to the dedicated invokers only.
+
+## Tagging Invokers
+Operators can configure any tags for invokers.
+
+```bash
+invoker0 ansible_host=${INVOKER01} tags="['dedicated']" dedicatedNamespaces="['namespace1']"
+invoker1 ansible_host=${INVOKER02} tags="['dedicated']" dedicatedNamespaces="['namespace2']"
+```
+
+Users can add the following annotations to their actions.
+
+```
+wsk action update params tests/dat/actions/params.js -i -a invoker-resources '["dedicated"]'
+```
+
+So this feature is based on the [tag-based-scheduling](./tag-based-scheduling.md).
+The `dedicatedNamespaces` field is used to make sure the invokers are not used by other than allowed namespaces and users can decide whether to run their actions on dedicated invokers using the `dedicated` tag.