README: Add missing http_archive import (#266)

Currently if you copy and paste the documented workspace methods you get a failure that `http_archive` is not specified: it needs to be imported.

Co-authored-by: lberki <[email protected]>

Author: edbaunton

README.md

@@ -76,6 +76,7 @@ If you are not using the Federation, you can simply import rules_python
 directly and call its initialization methods as follows:
 
 ```python
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 http_archive(
     name = "rules_python",
     url = "https://github.com/bazelbuild/rules_python/releases/download/0.0.1/rules_python-0.0.1.tar.gz",