Add a few comments on vendored dependencies

Rakefile

@@ -264,6 +264,9 @@ else
  lib.vendor_lib = "lib/bundler/vendor/molinillo"
  end
 
+ # We currently cherry-pick changes to use `require_relative` internally
+ # instead of regular `require`. These changes have been proposed upstream but
+ # haven't landed yet.
  desc "Vendor a specific version of thor"
  Automatiek::RakeTask.new("thor") do |lib|
  lib.download = { :github => "https://github.com/erikhuda/thor" }
@@ -272,6 +275,10 @@ else
  lib.vendor_lib = "lib/bundler/vendor/thor"
  end
 
+ # We currently cherry-pick changes to use `require_relative` internally
+ # instead of regular `require`. These changes have already landed to fileutils
+ # master, but have not yet been released, so we cherry-pick them for the time
+ # being.
  desc "Vendor a specific version of fileutils"
  Automatiek::RakeTask.new("fileutils") do |lib|
  lib.download = { :github => "https://github.com/ruby/fileutils" }
@@ -280,6 +287,8 @@ else
  lib.vendor_lib = "lib/bundler/vendor/fileutils"
  end
 
+ # We currently cherry-pick an unmerged PR on top of the upstream version:
+ # https://github.com/drbrain/net-http-persistent/pull/90.
  desc "Vendor a specific version of net-http-persistent"
  Automatiek::RakeTask.new("net-http-persistent") do |lib|
  lib.download = { :github => "https://github.com/drbrain/net-http-persistent" }