text: Title: [Doc]: Multipage PDF: unclear which backend supports and which does not support attach_note()
  Body: ### Documentation Link
  
  https://matplotlib.org/stable/gallery/misc/multipage_pdf.html
  
  ### Problem
  
  The issue is in the first two paragraphs of the page.
  
  > This is a demo of creating a pdf file with several pages, as well as adding metadata and annotations to pdf files.
  > 
  > If you want to use a multipage pdf file using LaTeX, you need to use from matplotlib.backends.backend_pgf import PdfPages. This version however does not support [attach_note](https://matplotlib.org/stable/api/backend_pdf_api.html#matplotlib.backends.backend_pdf.PdfPages.attach_note).
  
  Reading, it is unclear whether "this" in the last sentence refers to `pdf` backend (as suggested by it being on the page for it) or `pgf` (as suggested by it being in the paragraph about `pgf`).
  
  Only after clickking on the hyperlinked `attach_note` do I have to notice that it is a documentation page for a specific backend (which isn't obvious, being sent to an anchor in the middle of the document without header visible). From there, seeing that `pdf` has `attach_note()` I can infer that `pgf` doesn't. That string of logic is quite long for something that should have been clearly stated.
  
  ### Suggested improvement
  
  Change "this" to "that" in the last quoted sentence would probably make it clearer it is referring to the backend *not* used in the example. Or perhaps a different change in wording.