docs: use includes for command help output

docs/commands/create-userdir.md

@@ -0,0 +1,10 @@
+```
+usage: freqtrade create-userdir [-h] [--userdir PATH] [--reset]
+
+options:
+  -h, --help            show this help message and exit
+  --userdir PATH, --user-data-dir PATH
+                        Path to userdata directory.
+  --reset               Reset sample files to their original state.
+
+```