Slight adjustment to make smart_folding work — perhaps document?

[danielsgriffin]

Just installed. Excited this still works!
smart_folding wasn't working for me but global_folding was so I changed a line in the key bindings and it worked!
Note: just changed the operand in smart to match that in global: text.html.markdown

Not sure what it did but it made me happy.
old:

{ "keys": ["tab"], "command": "smart_folding", "context":
    [
        { "key": "selector", "operator": "equal", "operand": "markup.heading.markdown" }
    ]
},
{ "keys": ["shift+tab"], "command": "global_folding", "context":
    [
        { "key": "selector", "operator": "equal", "operand": "text.html.markdown" }
    ]
},

new:

{ "keys": ["tab"], "command": "smart_folding", "context":
    [
        { "key": "selector", "operator": "equal", "operand": "text.html.markdown" }
    ]
},
{ "keys": ["shift+tab"], "command": "global_folding", "context":
    [
        { "key": "selector", "operator": "equal", "operand": "text.html.markdown" }
    ]
},