Add exec flag to tmpfs

Many people who are using Docker also user the Code Server for Nextcloud Office. This requires tmp to be executable.
See nextcloud/docker#1896 (comment)

Signed-off-by: Thore Goebel <33295590+thgoebel@users.noreply.github.com>

Author: thgoebel

README.md

@@ -101,7 +101,7 @@ that adding an additional volume for /tmp speeds things up and eases the burden
     ...
     volumes:
       - type: tmpfs
-        target: /tmp
+        target: /tmp:exec
       ...
     ...
 ```