Add description for walrus codemod

src/codemodder/codemods/docs/pixee_python_use-walrus-if.md

@@ -0,0 +1,18 @@
+This codemod updates places where two separate statements involving an assignment
+and conditional can be replaced with a single Assignment Expression (commonly
+known as the walrus operator).
+
+Many developers use this operator in new code that they write but don't have
+the time to find and update every place in existing code. So we do it for you!
+We believe this leads to more concise and readable code.
+
+The changes from this codemod look like this:
+
+```diff
+- x = foo()
+- if x is not None:
++ if (x := foo()) is not None:
+      print(x)
+```
+
+The walrus operator is only supported in Python 3.8 and later.

src/codemodder/codemods/use_walrus_if.py

@@ -17,9 +17,7 @@ class UseWalrusIf(SemgrepCodemod, NameResolutionMixin):
         ScopeProvider,
     )
     NAME = "use-walrus-if"
-    SUMMARY = (
-        "Replace multiple expressions involving `if` operator with 'walrus' operator"
-    )
+    SUMMARY = "Use Assignment Expression in Conditional"
     REVIEW_GUIDANCE = ReviewGuidance.MERGE_AFTER_CURSORY_REVIEW
     DESCRIPTION = (
         "Replaces multiple expressions involving `if` operator with 'walrus' operator"

tests/test_codemod_docs.py

@@ -7,7 +7,7 @@
 @pytest.fixture(params=DEFAULT_CODEMODS)
 def codemod_name(request):
     name = request.param.name()
-    if name in ["order-imports", "use-walrus-if"]:
+    if name in ["order-imports"]:
         pytest.skip("No docs yet")
     return name