fix LiveDescriptors doc comment

[dlech]

Escape curly braces and fix spelling error.

Fixes the following warnings:

react-complex-tree/packages/core/src/types.ts:448:6 - warning Encountered an unescaped open brace without an inline tag
448     * of {variableName} can be used.
react-complex-tree/packages/core/src/types.ts:448:19 - warning Unmatched closing brace
448     * of {variableName} can be used.
react-complex-tree/packages/core/src/types.ts:450:7 - warning Encountered an unescaped open brace without an inline tag
450     * The {keybinding:bindingname} variable referns to a specific keybinding, i.e. {keybinding:primaryAction}
react-complex-tree/packages/core/src/types.ts:450:30 - warning Unmatched closing brace
450     * The {keybinding:bindingname} variable referns to a specific keybinding, i.e. {keybinding:primaryAction}
react-complex-tree/packages/core/src/types.ts:450:80 - warning Encountered an unescaped open brace without an inline tag
450     * The {keybinding:bindingname} variable referns to a specific keybinding, i.e. {keybinding:primaryAction}
react-complex-tree/packages/core/src/types.ts:450:105 - warning Unmatched closing brace
450     * The {keybinding:bindingname} variable referns to a specific keybinding, i.e. {keybinding:primaryAction}

Solves #TODO

@lukasbach

[lukasbach]

Thanks for the contribution!