Better explanation of blockHandler call filter (#136)

Author: schmidsi

pages/en/developer/create-subgraph-hosted.mdx

@@ -139,7 +139,7 @@ The important entries to update for the manifest are:
 
 - `dataSources.mapping.callHandlers`: lists the smart contract functions this subgraph reacts to and handlers in the mapping that transform the inputs and outputs to function calls into entities in the store.
 
-- `dataSources.mapping.blockHandlers`: lists the blocks this subgraph reacts to and handlers in the mapping to run when a block is appended to the chain. Without a filter, the block handler will be run every block. An optional filter can be provided with the following kinds: call`. A`call` filter will run the handler if the block contains at least one call to the data source contract.
+- `dataSources.mapping.blockHandlers`: lists the blocks this subgraph reacts to and handlers in the mapping to run when a block is appended to the chain. Without a filter, the block handler will be run every block. An optional call-filter can be provided by adding a `filter` field with `kind: call` to the handler. This will only run the handler if the block contains at least one call to the data source contract.
 
 A single subgraph can index data from multiple smart contracts. Add an entry for each contract from which data needs to be indexed to the `dataSources` array.