Add async backing parameters and fix image references

docs/maintain/maintain-guides-async-backing.md

@@ -13,7 +13,7 @@ slug: ../maintain-guides-async-backing
 This guide is relevant for cumulus based parachain projects started in 2023 or before. Later
 projects should already be async backing compatible. If starting a new parachain project, please use
 an async backing compatible template such as
-[`cumulus/parachain-template`](https://github.com/paritytech/cumulus/tree/rh-test-async-backing).
+[`cumulus/parachain-template`](https://github.com/paritytech/polkadot-sdk/tree/master/cumulus/parachain-template).
 
 :::
 
@@ -195,7 +195,7 @@ This phase consists of changes to your parachain’s runtime that activate async
 
 1. Increase the maximum `UNINCLUDED_SEGMENT_CAPACITY` in `runtime/src/lib.rs`.
 
-![Unincluded-segment-capacity](../assets/async/async-backing-unincluded-segment.png)
+![Unincluded-segment-capacity](../assets/async/async-backing-unincluded-segment-capacity.png)
 
 3. Decrease `MILLISECS_PER_BLOCK` to 6000.
 
@@ -214,6 +214,22 @@ This phase consists of changes to your parachain’s runtime that activate async
 
 ![minimum-period](../assets/async/async-backing-minimum-period.png)
 
+6. **Update parameters:** Once the runtime is deployed the final step is to update three parameters!
+
+After the runtime upgrade with async backing is activated there will be two new parameters:
+
+```json
+"async_backing_params": {
+    "max_candidate_depth": 0,
+    "allowed_ancestry_len": 0
+}
+```
+
+These need to be set to 3 and 2 respectively in governance for async backing to be enabled.
+
+⚠️ scheduling_lookahead must also be set to 2 along with this change otherwise parachain block times
+will degrade to worse than with sync backing! ⚠️
+
 ## Timing by Block Number
 
 With asynchronous backing it will be possible for parachains to opt for a block time of 6 seconds