Pylint warning and error fix in script

Changes:
   - C0114: Missing module docstring
   - C0116: Missing function or method docstring
   - C0209: Formatting a regular string which could be a f-string

Tested:
    - python3 -m pylint tools/robot_custom_rules.py

Change-Id: I6262db7919f3d64fd2012b2bdf8c2f0943f7f522
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/tools/robot_custom_rules.py b/tools/robot_custom_rules.py
index 7c7ddee..2b1c14c 100755
--- a/tools/robot_custom_rules.py
+++ b/tools/robot_custom_rules.py
@@ -1,7 +1,11 @@
 #!/usr/bin/env python3
-# Custom rules file for robotframework-lint.
-# Installation : pip3 install --upgrade robotframework-lint
-# Example usage: python3 -m rflint -rA robot_standards -R robot_custom_rules.py .
+r"""
+Custom rules file for robotframework-lint.
+Installation : pip3 install --upgrade robotframework-lint
+Example usage:
+    python3 -m rflint -rA robot_standards -R robot_custom_rules.py .
+"""
+
 import re
 
 from rflint.common import ERROR, SuiteRule
@@ -9,12 +13,16 @@
 
 class ExtendInvalidTable(SuiteRule):
     r"""
-    Extend robotframework-lint SuiteRule function for InvalidTable to allow a table section if it is
-    a section of comments. e.g "*** Comments ***"
+    Extend robotframework-lint SuiteRule function for InvalidTable to allow a
+    table section if it is a section of comments.
+    e.g "*** Comments ***"
     """
     severity = ERROR
 
     def apply(self, suite):
+        r"""
+        Walk through the code and report.
+        """
         for table in suite.tables:
             if not re.match(
                 r"^(settings?|metadata|(test )?cases?|(user"
@@ -24,6 +32,6 @@
             ):
                 self.report(
                     suite,
-                    "Unknown table name '%s'" % table.name,
+                    table.name,
                     table.linenumber,
                 )