add permutiveIdentityManagerIdSystem docs

dev-docs/modules/userid-submodules/permutiveIdentityManagerIdSystem.md

@@ -0,0 +1,65 @@
+---
+layout: userid
+title: Permutive Identity Manager
+description: Permutive Identity Manager User ID sub-module
+useridmodule: permutiveIdentityManagerIdSystem
+---
+
+# Permutive Identity Manager
+
+This module supports [Permutive](https://permutive.com/) customers in using Permutive's Identity Manager functionality.
+
+To use this Prebid.js module it is assumed that the site includes Permutive's SDK, with Identity Manager configuration
+enabled. See Permutive's user documentation for more information on Identity Manager.
+
+## Building Prebid.js with Permutive Identity Manager Support
+
+Prebid.js must be built with the `permutiveIdentityManagerIdSystem` module in order for Permutive's Identity Manager to be able to
+activate relevant user identities to Prebid.
+
+To build Prebid.js with the `permutiveIdentityManagerIdSystem` module included:
+
+```sh
+gulp build --modules=userId,permutiveIdentityManagerIdSystem
+```
+
+## Prebid configuration
+
+There is minimal configuration required to be set on Prebid.js, since the bulk of the behaviour is managed through
+Permutive's dashboard and SDK.
+
+It is recommended to keep the Prebid.js caching for this module short, since the mechanism by which Permutive's SDK
+communicates with Prebid.js is effectively a local cache anyway.
+
+```js
+pbjs.setConfig({
+  ...
+  userSync: {
+    userIds: [
+      {
+        name: 'permutiveIdentityManagerId',
+        params: {
+          ajaxTimeout: 90
+        },
+        storage: {
+          type: 'html5',
+          name: 'permutiveIdentityManagerId',
+          refreshInSeconds: 5
+        }
+      }
+    ],
+    auctionDelay: 100
+  },
+  ...
+});
+```
+
+### ajaxTimeout
+
+By default this module will read IDs provided by the Permutive SDK from local storage when requested by prebid, and if
+nothing is found, will not provide any identities. If a timeout is provided via the `ajaxTimeout` parameter, it will
+instead wait for up to the specified number of milliseconds for Permutive's SDK to become available, and will retrieve
+identities from the SDK directly if/when this happens.
+
+This value should be set to a value smaller than the `auctionDelay` set on the `userSync` configuration object, since
+there is no point waiting longer than this as the auction will already have been triggered.