add (overwrite with) mypy stubs, if available

builtins/3/pwd.pyi

@@ -0,0 +1,18 @@
+# Stubs for pwd
+
+# NOTE: These are incomplete!
+
+import typing
+
+class struct_passwd:
+    # TODO use namedtuple
+    pw_name = ''
+    pw_passwd = ''
+    pw_uid = 0
+    pw_gid = 0
+    pw_gecos = ''
+    pw_dir = ''
+    pw_shell = ''
+
+def getpwuid(uid: int) -> struct_passwd: ...
+def getpwnam(name: str) -> struct_passwd: ...