Improve readme

README.md

@@ -19,12 +19,18 @@ The recommended way is:
 * Put the signed file in `~/.pdf_signatures/`.
 
 You can now use the `pdf-sign` tool interactively (or non-interactively) to sign PDF files.
+The GUI is self documented and allows both keyboard-only and pointer-only operation.
 
 Run `pdf-sign -h` or `pdf-create-empty -h` for details.
 
 **Installation**
 
-* Install dependencies: `python3.7` or later with module `tkinter`, `gs` (Ghostscript), `pdftk` and `pdfinfo`.
+* Install dependencies
+  * `python3.7` or later
+  * Python module `tkinter` (only needed for interactive use)
+  * `gs` (Ghostscript)
+  * `pdftk`
+  * `pdfinfo`
 * Copy one or both tools to a directory in your `$PATH`.
 
 **Installation on Debian**