build: add README.md to the SSR ng_package

Adds a readme to the npm package

(cherry picked from commit 439c463)

Author: alan-agius4

packages/angular/ssr/BUILD.bazel

@@ -61,6 +61,7 @@ ng_package(
         "//packages/angular/ssr/third_party/beasties:beasties_dts",
     ],
     package = "@angular/ssr",
+    readme_md = ":README.md",
     rollup_runtime_deps = [
         "//:node_modules/@babel/core",
         "//:node_modules/@rollup/plugin-commonjs",