Properly escape sed replace expressions

This fixes an error during container startup due to interpolating a
$STORAGE value that may contain slashes or other "active" characters:

    ...
    Using secure websockets: false
    Using storage adapter: ./storage/file
    sed: bad option in substitution expression

Also add a trailing ',' in the search expression to avoid substituting
in the comment above the actual definition:

    /*  If Cryptpad is proxied without using https, the server needs to know.
     *  Specify 'useSecureWebsockets: true' so that it can send
    ...

docs/cryptpad-docker.md

@@ -22,15 +22,6 @@ Or, using docker-compose
 docker-compose up -d
 ```
 
-## TODO
-
-```
-cryptpad_1  | Linking config.js
-cryptpad_1  | Using secure websockets: true
-cryptpad_1  | Using storage adapter: './storage/file'
-cryptpad_1  | sed: -e expression #1, char 27: unknown option to `s'
-```
-
 ## Configuration
 
 Set configurations Dockerfile or in .env (using docker-compose) file.