changes to pip_repository source files now re-trigger the repo rule (#601)

* changes to pip_repository source files now re-trigger the repo rule

* update diff test message.

* added note about auto-gen.

* Updated docs

* remove unnecessary snippet

* installer -> updater

Co-authored-by: Jonathon Belotti <jonathon@canva.com>

python/BUILD

diff --git a/python/BUILD b/python/BUILD
index 96df383..7dbbec3 100644
--- a/python/BUILD
+++ b/python/BUILD
@@ -46,6 +46,7 @@
         "defs.bzl",
         "packaging.bzl",
         "pip.bzl",
+        "//python/pip_install:bzl",
         "//python/private:bzl",
     ],
     visibility = ["//:__pkg__"],