Move pages under tldr, lint run.sh, update docs

tldr/flask

@@ -0,0 +1,21 @@
+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# flask
+
+> A general utility script for Flask applications. Loads the application defined in the `FLASK_APP` environment variable.
+> More information: <https://flask.palletsprojects.com/en/1.1.x/cli/>.
+
+- Run a development server:
+
+`flask run`
+
+- Show the routes for the app:
+
+`flask routes`
+
+- Run a Python interactive shell in the app's context:
+
+`flask shell`