Add docs for indexer hints (#583)

Author: incrypto32

website/pages/en/developing/creating-a-subgraph.mdx

@@ -101,6 +101,8 @@ description: Gravatar for Ethereum
 repository: https://github.com/graphprotocol/graph-tooling
 schema:
   file: ./schema.graphql
+indexerHints:
+  prune: auto
 dataSources:
   - kind: ethereum/contract
     name: Gravity
@@ -150,6 +152,37 @@ The important entries to update for the manifest are:
 
 - `features`: a list of all used [feature](#experimental-features) names.
 
+- `indexerHints.prune`: Defines the retention of historical block data for a subgraph. Options include:
+
+  1. `"never"`: No pruning of historical data; retains the entire history.
+  2. `"auto"`: Retains the minimum necessary history as set by the indexer, optimizing query performance.
+  3. A specific number: Sets a custom limit on the number of historical blocks to retain.
+
+  ```
+   indexerHints:
+    prune: auto
+  ```
+
+  > The term "history" in this context of subgraphs is about storing data that reflects the old states of mutable entities. This capability is essential for [time travel queries](/querying/graphql-api/#time-travel-queries), This feature enables querying the past states of these entities at specific blocks throughout the blockchain's history.
+
+  Using `"auto"` is generally recommended as it maximizes query performance and is sufficient for most users who do not require access to extensive historical data.
+
+  For subgraphs leveraging [time travel queries](/querying/graphql-api/#time-travel-queries), it's advisable to either set a specific number of blocks for historical data retention or use `prune: never` to keep all historical entity states. Below are examples of how to configure both options in your subgraph's settings:
+
+  To retain a specific amount of historical data:
+
+  ```
+   indexerHints:
+    prune: 1000 # Replace 1000 with the desired number of blocks to retain
+  ```
+
+  To preserve the complete history of entity states:
+
+  ```
+  indexerHints:
+    prune: never
+  ```
+
 - `dataSources.source`: the address of the smart contract the subgraph sources, and the ABI of the smart contract to use. The address is optional; omitting it allows to index matching events from all contracts.
 
 - `dataSources.source.startBlock`: the optional number of the block that the data source starts indexing from. In most cases, we suggest using the block in which the contract was created.