feat: add documentation about ComputingElement

Author: aldbr

docs/source/DeveloperGuide/AddingNewComponents/Resources/Computing.rst

@@ -0,0 +1,5 @@
+----------------
+ComputingElement
+----------------
+
+The full code documentation is available here :py:class:`~DIRAC.Resources.Computing.ComputingElement`

docs/source/DeveloperGuide/AddingNewComponents/Resources/index.rst

@@ -16,5 +16,6 @@ DIRAC applications
    :maxdepth: 2
 
    Catalog
+   Computing
    MessageQueues/index
    Storage

src/DIRAC/Resources/Computing/ComputingElement.py

@@ -19,6 +19,17 @@
 
      The ComputingElement objects are usually instantiated with the help of
      ComputingElementFactory.
+
+     The ComputingElement class can be considered abstract. 3 kinds of abstract ComputingElements
+     can be distinguished from it:
+
+      - Remote ComputingElement: includes methods to interact with a remote ComputingElement
+        (e.g. HtCondorCEComputingElement, ARCComputingElement).
+      - Inner ComputingElement: includes methods to locally interact with an underlying worker node.
+        It is worth noting that an Inner ComputingElement provides synchronous submission
+        (the submission of a job is blocking the execution until its completion). It deals with one job at a time.
+      - Inner Pool ComputingElement: includes methods to locally interact with Inner ComputingElements asynchronously.
+        It can manage a pool of jobs running simultaneously.
 """
 
 import os