docs(composite): add composite key docs (#968)

docs/pages/docs/walkthrough/_meta.json

@@ -13,5 +13,6 @@
   "relations": "",
   "raw": "",
   "transactions": "",
+  "composite": "",
   "limitations": ""
 }

docs/pages/docs/walkthrough/composite.md

@@ -0,0 +1,69 @@
+# Composite
+
+## Composite queries
+
+The examples use the following prisma schema:
+
+```prisma
+model Organization {
+  platformId   String
+  platformKind String
+
+  name String
+
+  repositories Repository[]
+
+  @@unique(name: "organization_name", [platformId, name])
+
+  // Compose the primary key with the platformKind and platformId fields
+  @@id(name: "organization_id", [platformKind, platformId])
+}
+
+model Repository {
+  platformId   String
+  platformKind String
+
+  orgId String?
+  org   Organization? @relation(fields: [platformKind, orgId], references: [platformKind, platformId])
+
+  // Compose the primary key with the platformKind and platformId fields
+  @@id(name: "repository_id", [platformKind, platformId])
+}
+```
+
+## Composite keys
+
+You can query for composite keys using the composite key id, whether it is a unique or primary key.
+
+```go
+// query by primary key
+org, err := client.Organization.FindUnique(
+  Organization.OrganizationID( // @@id(name: "organization_id", ...) maps to .OrganizationID
+    Organization.PlatformKind.Equals("private"),
+    Organization.PlatformID.Equals("123"),
+  ),
+).Exec(ctx)
+```
+
+```go
+// query by unique key
+org, err := client.Organization.FindUnique(
+  Organization.OrganizationName( // @@id(name: "organization_name", ...) maps to .OrganizationName
+    Organization.PlatformID.Equals("test"),
+    Organization.Name.Equals("test"),
+  ),
+).Exec(ctx)
+```
+
+## Create with composite primary keys
+
+To create records with a composite primary key, just specify the fields in the correct order. You don't have to
+explicitly specify the composite key name.
+
+```go
+org, err = client.Organization.CreateOne(
+  Organization.PlatformID.Set("123"),
+  Organization.PlatformKind.Set("private"),
+  Organization.Name.Set("test"),
+).Exec(ctx)
+```