Add doc-strings

Signed-off-by: akugarg <akanksha.garg2k@gmail.com>

Author: akugarg

src/licensedcode/plugin_license.py

@@ -129,7 +129,9 @@ def process_codebase(self, codebase, **kwargs):
 
 def match_reference_license(resource, codebase):
     """
-    Return the updated license matches having reference to another files
+    Return the ``resource`` Resource updating and saving it in place, after adding new
+    icense matches (licenses and license_expressions) following their Rule
+    ``referenced_filenames`` if any. Return None if this is not a file Resource.
     """
     if not resource.is_file:
         return
@@ -142,16 +144,20 @@ def match_reference_license(resource, codebase):
     referenced_licenses = []
     referenced_license_expressions = []
     referenced_filenames = get_referenced_filenames(licenses)
+    modified = False
 
     for referenced_filename in referenced_filenames:
         new_resource = find_referenced_resource(referenced_filename=referenced_filename, resource=resource, codebase=codebase)
         if new_resource:
+            modified = True
             referenced_licenses.extend(new_resource.licenses)
             referenced_license_expressions.extend(new_resource.license_expressions)
 
     licenses.extend(referenced_licenses)
     license_expressions.extend(referenced_license_expressions)
-    codebase.save_resource(resource)
+    
+    if modified:
+        codebase.save_resource(resource)
     return resource
 
 
@@ -171,7 +177,9 @@ def get_referenced_filenames(license_matches):
 
 def find_referenced_resource(referenced_filename, resource, codebase, **kwargs):
     """
-    Return the resource object for matching referenced-filename given a resource in codebase
+    Return a Resource matching the ``referenced_filename`` path or filename given a ``resource`` in ``codebase``.
+    Return None if the ``referenced_filename`` cannot be found in the same directory as the base ``resource``.
+    ``referenced_filename`` is the path or filename referenced in a LicenseMatch of ``resource``,
     """
     parent = resource.parent(codebase)