Add example of an application with an .ini file and paste_prefix.

Issue: Pylons#146

examples/pserve_ini_app/app.py

@@ -0,0 +1,42 @@
+import os
+import sys
+
+from pyramid.config import Configurator
+from pyramid.request import Request
+from pyramid.scripts.pserve import main
+from pyramid.view import view_config
+
+APP_FOLDER = os.path.dirname(__file__)
+
+
+@view_config(route_name="version", renderer="json", request_method="GET", openapi=True)
+def get(request: Request):
+    """Get the app's version."""
+    return {"Version": "0.0.1"}
+
+
+def wsgi_app(global_config, **settings):
+    """Prepare a Pyramid app."""
+    with Configurator() as config:
+        config.include("pyramid_openapi3")
+        config.pyramid_openapi3_spec(
+            os.path.join(APP_FOLDER, "openapi.yaml")
+        )
+        config.pyramid_openapi3_add_explorer()
+        config.add_route("version", "/version")
+        config.scan(".")
+
+        return config.make_wsgi_app()
+
+
+if __name__ == '__main__':
+    # The normal way of starting an app would be `pserve server.ini`
+    # we replicate this here by adding a sys.argv
+
+    # normally you'd have an egg or a proper package, but this app is simpler.
+    # This way can only work when the working directory is the same as where app.py is
+    # because of the hardcoded app:wsgi_app in server.ini
+    os.chdir(APP_FOLDER)
+    config_file = os.path.join(APP_FOLDER, 'server.ini')
+    sys.argv.append(config_file)
+    sys.exit(main())

examples/pserve_ini_app/openapi.yaml

@@ -0,0 +1,37 @@
+openapi: "3.0.0"
+
+servers:
+  - url: '/v'
+
+info:
+  version: "1.0.0"
+  title: A simple Todo app API
+
+paths:
+  /version:
+    get:
+      summary: version
+      description: version
+      tags:
+        - version
+      responses:
+        "200":
+          description: version
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/Item"
+
+
+components:
+
+  schemas:
+
+    Item:
+      type: object
+      required:
+        - title
+      properties:
+        title:
+          type: string
+          maxLength: 40

examples/pserve_ini_app/server.ini

@@ -0,0 +1,20 @@
+######
+# app configuration
+# https://docs.pylonsproject.org/projects/pyramid/en/latest/narr/environment.html
+######
+[app:test-app]
+paste.app_factory = app:wsgi_app
+
+[filter:paste_prefix]
+use = egg:PasteDeploy#prefix
+prefix = /v
+
+[pipeline:main]
+pipeline =
+    paste_prefix
+    test-app
+
+[server:main]
+use = egg:waitress#main
+host = 0.0.0.0
+port = 6543