DOC: add documentation for extract-annotated-pages subcommand

Issue: #95

Author: moormaster

docs/index.rst

@@ -16,6 +16,7 @@ pdfly is a command line tool to get information about PDF documents and to manip
    user/subcommand-meta
    user/subcommand-cat
    user/subcommand-x2pdf
+   user/subcommand-extract-annotated-pages
    user/subcommand-extract-images
    user/subcommand-2-up
    user/subcommand-booklet

docs/user/subcommand-extract-annotated-pages.md

@@ -0,0 +1,44 @@
+# extract-annotated-pages
+
+Extract only the annotated pages from a PDF. This can help to review or rework pages from a large document iteratively.
+
+## Usage
+
+```
+pdfly extract-annotated-pages --help
+
+ Usage: pdfly extract-annotated-pages [OPTIONS] INPUT_PDF
+
+ Extract only the annotated pages from a PDF.
+
+ Q: Why does this help?
+ A: https://github.com/py-pdf/pdfly/issues/97
+
+╭─ Arguments ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
+│ *    input_pdf      FILE  Input PDF file. [required]                                                                             │
+╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
+╭─ Options ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
+│ --output  -o      PATH  Output PDF file. Defaults to 'input_pdf_annotated'.                                                      │
+│ --help                  Show this message and exit.                                                                              │
+╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
+
+```
+
+## Examples
+
+### Input file
+
+Extracts only pages containing annotations from a file `input.pdf`. Pages are written into a new file `input_annotated.pdf`.
+
+```
+pdfly extract-annotated-pages input.pdf
+```
+
+### Input file with specific output file
+
+Extracts only pages containing annotations from a file `input.pdf` into the given output file `pages_to_rework.pdf`.
+
+
+```
+pdfly extract-annotated-pages input.pdf -o pages_to_rework.pdf
+```