message: Document that build-tools exists
  ## Description
  Update list of lerna managed release groups to include build-tools.
diff: @@ -44,6 +44,8 @@ Here's the list of Lerna managed release groups:
  - [Packages](./server/gitrest/packages) (Published in the `@fluidframework/` namespace)
  - historian (Rooted in [./server/historian](./server/historian). Configured by [./server/historian/lerna.json](./server/historian/lerna.json))
  - [Packages](./server/historian/packages) (Published in the `@fluidframework/` namespace)
  +- build-tools (Rooted in [./build-tools](./build-tools). Configured by [./build-tools/lerna.json](./build-tools/lerna.json))
  + - [Packages](./build-tools/packages) (Published in a mix of `@fluidframework/` and `@fluid-tools/` namespaces)
  Here's a list of other sets of other packages (each package within these groups is versioned independently,
  forming its own release group):
  