Add notice of requesting source code in rkpd

Flag: EXEMPT license change for b/418865751
Bug: 418865751
Test: presubmits
Test: lunch husky-trunk_staging-eng && m, an extra line is added at the top of NOTICE.html file in NOTICE.html.gz
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:58fa087736d87ca3bfc5589a248d5d49ec3d3b76)
Merged-In: I999bea0f1e3180216c05212aad2da9e4ac37303f
Change-Id: I999bea0f1e3180216c05212aad2da9e4ac37303f