message: CXX-1304 Document std::experimental polyfill as unsupported
diff: @@ -57,7 +57,10 @@ implementations for these features:
  Select with `-DBSONCXX_POLY_USE_STD_EXPERIMENTAL=1`. If your
  toolchain's standard library provides `optional` and
  `string_view` in the namespace `std::experimental`, you can use
  - this option.
  + this option. Be aware that your standard library's
  + `std::experimental` implementation may change over time,
  + breaking binary compatibility in unexpected ways. Note that this
  + polyfill is *not* recommended and is unsupported.
  Most users should be fine sticking with the default. However, if you
  have an existing application which makes heavy use of one of the
  @@ -67,9 +70,6 @@ against the same library.
  **DO NOT** change your project's polyfill if you need to create a
  stable binary interface.
  -Be aware that your standard library's `std::experimental` implementation
  -may change over time, breaking binary compatibility in unexpected ways.
  -
  ### Step 3: Download the latest version of the mongocxx driver.
  To get the source via git, the `releases/stable` branch will track the most
  