Update docs about package name specification (#3257)

Updated documentation for more specification about module and project names, due to ModuleOrPackagesNotFound uncertainty.

Co-authored-by: Steph Samson <hello@stephsamson.com>
Co-authored-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>

docs/basic-usage.md

@@ -55,6 +55,11 @@ requires = ["poetry-core"]
 build-backend = "poetry.core.masonry.api"
 ```
 
+Poetry assumes your package contains a package with the same name as `tool.poetry.name`.
+If this is not the case, populate `tool.poetry.packages` to specify your package or packages.
+
+See [Packages](/docs/pyproject#packages) for more information.
+
 ### Initialising a pre-existing project
 
 Instead of creating a new project, Poetry can be used to 'initialise' a pre-populated