Updates to EMBER documentation

[nehatk17]

1. Add instructions for uploading external video files

If using video files, replace dandi organize "source folder" with

dandi organize --update-external-file-paths --files-mode copy /path/to/source_folder

2. Update Javascript to enable drop-down and nested drop-down sections (set up python section, my files are all NWB/BIDS compatible, new to python, used DANDI/CLI tools before) and callout sections (examples: check if files can be converted to NWB, password prompt paragraph)

[nehatk17]

Example for password prompt -> end of documentation

Warning

Password Prompt
If this is your first upload, you may get a prompt to enter a password in step 4. In the EMBER-DANDI Portal, click on your user icon in the top right to retrieve your API key. Enter this when prompted for your password. (include image of API key)