message: Improve docs by describing the purpose of the commands
diff: @@ -18,6 +18,8 @@ npm install -g apollo-codegen
  ### `introspect-schema`
  +The purpose of this command is to create a JSON introspection dump file for a given graphql schema. The input schema can be fetched from a remote graphql server or from a local file. The resulting JSON introspection dump file is needed as input to the [generate](#generate) command.
  +
  To download a GraphQL schema by sending an introspection query to a server:
  ```sh
  @@ -38,6 +40,8 @@ apollo-codegen introspect-schema schema.graphql --output schema.json
  ### `generate`
  +The purpose of this command is to generate types for query and mutation operations made against the schema (it will not generate types for the schema itself).
  +
  This tool will generate Swift code by default from a set of query definitions in `.graphql` files:
  ```sh
  @@ -48,11 +52,11 @@ You can also generate type annotations for TypeScript, Flow, or Scala using the
  ```sh
  # TypeScript
  -apollo-codegen generate **/*.graphql --schema schema.json --target typescript --output schema.ts
  +apollo-codegen generate **/*.graphql --schema schema.json --target typescript --output operation-result-types.ts
  # Flow
  -apollo-codegen generate **/*.graphql --schema schema.json --target flow --output schema.flow.js
  +apollo-codegen generate **/*.graphql --schema schema.json --target flow --output operation-result-types.flow.js
  # Scala
  -apollo-codegen generate **/*.graphql --schema schema.json --target scala --output schema.scala
  +apollo-codegen generate **/*.graphql --schema schema.json --target scala --output operation-result-types.scala
  ```
  #### `gql` template support
  