add options variable to isort

doc/ale-python.txt

@@ -145,6 +145,14 @@ g:ale_python_isort_executable                   *g:ale_python_isort_executable*
   See |ale-integrations-local-executables|
 
 
+g:ale_python_isort_options                      *g:ale_python_isort_options*
+                                                *b:ale_python_isort_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be set to pass extra options to isort.
+
+
 g:ale_python_isort_use_global                   *g:ale_python_isort_use_global*
                                                 *b:ale_python_isort_use_global*
   Type: |Number|