Add a couple of docstrings

These are based on observation of the outputs of these functions.

jedi/inference/param.py

@@ -51,6 +51,25 @@ class ExecutedParamName(ParamName):
 
 
 def get_executed_param_names_and_issues(function_value, arguments):
+    """
+    Return a tuple of:
+      - a list of `ExecutedParamName`s corresponding to the arguments of the
+        function execution `function_value`, containing the inferred value of
+        those arguments (whether explicit or default)
+      - a list of the issues encountered while building that list
+
+    For example, given:
+    ```
+    def foo(a, b, c=None, d='d'): ...
+
+    foo(42, c='c')
+    ```
+
+    Then for the execution of `foo`, this will return a tuple containing:
+      - a list with entries for each parameter a, b, c & d; the entries for a,
+        c, & d will have their values (42, 'c' and 'd' respectively) included.
+      - a list with a single entry about the lack of a value for `b`
+    """
     def too_many_args(argument):
         m = _error_argument_count(funcdef, len(unpacked_va))
         # Just report an error for the first param that is not needed (like
@@ -207,6 +226,23 @@ def get_executed_param_names_and_issues(function_value, arguments):
 
 
 def get_executed_param_names(function_value, arguments):
+    """
+    Return a list of `ExecutedParamName`s corresponding to the arguments of the
+    function execution `function_value`, containing the inferred value of those
+    arguments (whether explicit or default). Any issues building this list (for
+    example required arguments which are missing in the invocation) are ignored.
+
+    For example, given:
+    ```
+    def foo(a, b, c=None, d='d'): ...
+
+    foo(42, c='c')
+    ```
+
+    Then for the execution of `foo`, this will return a list containing entries
+    for each parameter a, b, c & d; the entries for a, c, & d will have their
+    values (42, 'c' and 'd' respectively) included.
+    """
     return get_executed_param_names_and_issues(function_value, arguments)[0]