Add a link to the labs feature documentation

Signed-off-by: Aaron Raimist <aaron@raim.ist>

src/components/views/settings/tabs/user/LabsUserSettingsTab.js

@@ -49,6 +49,15 @@ export default class LabsUserSettingsTab extends React.Component {
         return (
             <div className="mx_SettingsTab">
                 <div className="mx_SettingsTab_heading">{_t("Labs")}</div>
+                <div className='mx_SettingsTab_subsectionText'>
+                    {
+                        _t('These are experimental features. For more information on what ' +
+                            'these options do see <a>the documentation</a>.', {}, {
+                            'a': (sub) => <a href="https://github.com/vector-im/riot-web/blob/develop/docs/labs.md"
+                                             rel='noopener' target='_blank'>{sub}</a>,
+                        })
+                    }
+                </div>
                 <div className="mx_SettingsTab_section">
                     {flags}
                     <SettingsFlag name={"enableWidgetScreenshots"} level={SettingLevel.ACCOUNT} />

src/i18n/strings/en_EN.json

@@ -641,6 +641,7 @@
     "Access Token:": "Access Token:",
     "click to reveal": "click to reveal",
     "Labs": "Labs",
+    "These are experimental features. For more information on what these options do see <a>the documentation</a>.": "These are experimental features. For more information on what these options do see <a>the documentation</a>.",
     "Ignored/Blocked": "Ignored/Blocked",
     "Error adding ignored user/server": "Error adding ignored user/server",
     "Something went wrong. Please try again or view your console for hints.": "Something went wrong. Please try again or view your console for hints.",