Fix typo in README (#3531)

culsters -> clusters

Author: eltociear

README.md

@@ -397,7 +397,7 @@ replacement = {
 
 You can see that we have replaced `ElectricalMeasurement.cluster_id` from endpoint 1 in the `signature` dict with the name of our cluster that we created: `ElectricalMeasurementCluster` and on endpoint 2 we replaced `AnalogInput.cluster_id` with the implementation we created for that: `AnalogInputCluster`. This instructs Zigpy to use these `CustomCluster` derivatives instead of the normal cluster definitions for these clusters and this is why this part of the quirk is called `replacement`.
 
-Now lets put this all together. If you examine the device definition above you will see that we have defined our custom device, we defined the `signature` dict where we transcribed the `SimpleDescriptor` output we obtained when the device joined the network and we defined the `replacement` dict where we swapped the cluster ids for the culsters that we wanted to replace with the `CustomCluster` implementations that we created.
+Now lets put this all together. If you examine the device definition above you will see that we have defined our custom device, we defined the `signature` dict where we transcribed the `SimpleDescriptor` output we obtained when the device joined the network and we defined the `replacement` dict where we swapped the cluster ids for the clusters that we wanted to replace with the `CustomCluster` implementations that we created.
 
 # Contribution Guidelines