Add entry for "hold to walk" in keybinds settings menu

[GeckoEidechse]

So in case you didn't know, one can bind a key to +walk, i.e. bind "LCTRL" "+walk". This is especially useful when using autosprint, as it allows you to go from sprinting to walking while holding LCTRL in this example.

I'm not sure how easy it is to add additional keybinds but if possible I think it makes sense to add an entry to set a key for +walk in the keybind options.