docs: add user stories

.gitignore

@@ -117,3 +117,5 @@ app.*.symbols
 !**/ios/**/default.perspectivev3
 !/packages/flutter_tools/test/data/dart_dependencies_test/**/.packages
 !/dev/ci/**/Gemfile.lock
+
+docs/.*

README.md

@@ -1,2 +1,3 @@
 # pdf_signature
-create a signature on pdf page
+
+A GUI app to create a signature on PDF page interactively.

docs/FRs.md

@@ -0,0 +1,24 @@
+# Functional Requirements
+
+## user stories
+
+* name: PDF browser
+  * role: user
+  * functionality: view and navigate PDF documents
+  * benefit: select page to add signature
+* name: load signature picture
+  * role: user
+  * functionality: load a signature picture file
+  * benefit: easily add signature to PDF
+* name: geometrically adjust signature picture
+  * role: user
+  * functionality: adjust the size and position of the signature picture
+  * benefit: ensure the signature fits well on the PDF page
+* name: graphically adjust signature picture
+  * role: user
+  * functionality: background removal, contrast adjustment...
+  * benefit: easily improve the appearance of the signature on the PDF without additional software.
+* name: draw signature
+  * role: user
+  * functionality: draw a signature using mouse or touch input
+  * benefit: create a custom signature directly on the PDF if no pre-made signature is available.

docs/use_cases.md

@@ -0,0 +1,4 @@
+# Use cases
+
+Use cases are generated from `FRs.md`, and `meta-arch.md` in `gherkin` format.
+