Add bf cli dialog merge instructions to generator usage docs

[benbrown]

After generating a bot from the yeoman templates using the command line tools, a bf cli command has to be run to generate and merge the schema files, and process any installed components.

We should add instructions to this file and other relevant doc locations.

The bf cli command that needs to be run from inside the project folder:

bf dialog:merge [package.json or .csproj] --imports ../dialogs/imported --output ../schemas/sdk

• note when we add these we should make sure to check that this is the latest syntax for everything