Add docs for DataSourceContext in manifest (#520)

Author: incrypto32

website/pages/en/developing/assemblyscript-api.mdx

@@ -808,6 +808,61 @@ The base `Entity` class and the child `DataSourceContext` class have helpers to
 - `getBoolean(key: string): boolean`
 - `getBigDecimal(key: string): BigDecimal`
 
+### DataSourceContext in Manifest
+
+The `context` section within `dataSources` allows you to define key-value pairs that are accessible within your subgraph mappings. The available types are `Bool`, `String`, `Int`, `Int8`, `BigDecimal`, `Bytes`, `List`, and `BigInt`.
+
+Here is a YAML example illustrating the usage of various types in the `context` section:
+
+```yaml
+dataSources:
+  - kind: ethereum/contract
+    name: ContractName
+    network: mainnet
+    context:
+      bool_example:
+        type: Bool
+        data: true
+      string_example:
+        type: String
+        data: 'hello'
+      int_example:
+        type: Int
+        data: 42
+      int8_example:
+        type: Int8
+        data: 127
+      big_decimal_example:
+        type: BigDecimal
+        data: '10.99'
+      bytes_example:
+        type: Bytes
+        data: '0x68656c6c6f'
+      list_example:
+        type: List
+        data:
+          - type: Int
+            data: 1
+          - type: Int
+            data: 2
+          - type: Int
+            data: 3
+      big_int_example:
+        type: BigInt
+        data: '1000000000000000000000000'
+```
+
+- `Bool`: Specifies a Boolean value (`true` or `false`).
+- `String`: Specifies a String value.
+- `Int`: Specifies a 32-bit integer.
+- `Int8`: Specifies an 8-bit integer.
+- `BigDecimal`: Specifies a decimal number. Must be quoted.
+- `Bytes`: Specifies a hexadecimal string.
+- `List`: Specifies a list of items. Each item needs to specify its type and data.
+- `BigInt`: Specifies a large integer value. Must be quoted due to its large size.
+
+This context is then accessible in your subgraph mapping files, enabling more dynamic and configurable subgraphs.
+
 ### Common AssemblyScript Issues
 
 There are certain [AssemblyScript](https://github.com/AssemblyScript/assemblyscript) issues that are common to run into during subgraph development. They range in debug difficulty, however, being aware of them may help. The following is a non-exhaustive list of these issues:

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

@@ -109,6 +109,13 @@ dataSources:
       address: '0x2E645469f354BB4F5c8a05B3b30A929361cf77eC'
       abi: Gravity
       startBlock: 6175244
+    context:
+      foo:
+        type: Bool
+        data: true
+      bar:
+        type: String
+        data: 'bar'
     mapping:
       kind: ethereum/events
       apiVersion: 0.0.6
@@ -146,6 +153,8 @@ The important entries to update for the manifest are:
 
 - `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.
 
+- `dataSources.context`: key-value pairs that can be used within subgraph mappings. Supports various data types like `Bool`, `String`, `Int`, `Int8`, `BigDecimal`, `Bytes`, `List`, and `BigInt`. Each variable needs to specify its `type` and `data`. These context variables are then accessible in the mapping files, offering more configurable options for subgraph development.
+
 - `dataSources.mapping.entities`: the entities that the data source writes to the store. The schema for each entity is defined in the schema.graphql file.
 
 - `dataSources.mapping.abis`: one or more named ABI files for the source contract as well as any other smart contracts that you interact with from within the mappings.