Add privacy disclaimer

I haven't had a chance to test this, because I don't currently have a fully functioning computer I can set up a dev-environment on, but this *should* make it so when a user toggles a post to be private, a disclaimer appears clarifying what "private" really means.

app/assets/javascripts/components/features/compose/components/compose_form.jsx

@@ -175,6 +175,13 @@ const ComposeForm = React.createClass({
           <Toggle checked={this.props.private} onChange={this.handleChangeVisibility} />
           <span className='compose-form__label__text'><FormattedMessage id='compose_form.private' defaultMessage='Mark as private' /></span>
         </label>
+       
+        <Motion defaultStyle={{ opacity: 0, height: 0 }}, style={{ opacity: spring((this.props.private || reply_to_other) ? 0 : 100), height: spring((this.props.private || reply_to_other) ? 0 : 39.5) }}>
+            <label className='compose-form__label' style={{ height: `${height}px`, overflow: 'hidden', opacity: opacity / 100 }}>
+              <span className='compose-form__label__text'><FormattedMessage id='compose_form.privacy_disclaimer' defaultMessage='Warning: Private posts are not encrypted, and could be read or boosted by instances or people who do not respect post privacy. This is not true privacy. Do not post senstive information.' /></span>
+            </label>
+          }
+        </Motion>
 
         <Motion defaultStyle={{ opacity: (this.props.private || reply_to_other) ? 0 : 100, height: (this.props.private || reply_to_other) ? 39.5 : 0 }} style={{ opacity: spring((this.props.private || reply_to_other) ? 0 : 100), height: spring((this.props.private || reply_to_other) ? 0 : 39.5) }}>
           {({ opacity, height }) =>