edk2_invocable.py: Improve documentation (#786)

Improve the in-line documentation for edk2_invocable.py, which improves the quality of documentation at https://www.tianocore.org/edk2-pytool-extensions/

edk2toolext/edk2_invocable.py

@@ -76,7 +76,7 @@ def GetSkippedDirectories(self) -> Tuple[str]:
  """
 
  def GetWorkspaceRoot(self) -> str:
- """Return the workspace root for initializing the SDE.
+ """Return the workspace root for initializing the SDE, will be mapped as edk2 WORKSPACE.
 
  !!! tip
  Required Override in a subclass
@@ -89,11 +89,19 @@ def GetWorkspaceRoot(self) -> str:
  raise NotImplementedError()
 
  def GetPackagesPath(self) -> Iterable[os.PathLike]:
- """Provides an iterable of paths should should be mapped as edk2 PackagePaths.
+ """Provides an iterable of paths which will be mapped as edk2 PACKAGES_PATH.
 
  !!! tip
  Optional Override in a subclass
 
+ Path can be,
+ 1. Absolute or
+ 2. Relative to WORKSPACE or
+ 3. Relative to current working dir
+
+ See Also,
+ https://github.com/tianocore/tianocore.github.io/wiki/Multiple_Workspace
+
  Returns:
  (Iterable[os.PathLike]): paths
  """