Add note that there is nothing to commit in git status plugin (#863)

* Add note that there is nothing to commit

* Fix lint

Author: drew-gross

src/plugins/GitStatus.tsx

@@ -445,6 +445,7 @@ class GitStatusComponent extends React.Component<GitStatusProps, GitStatusState>
 
     return <div style={{ padding: "10px" }}>
       <div>{branchText}</div>
+      {this.state.gitStatus.length === 0 ? <div>Nothing to commit, working tree clean.</div> : undefined}
       <GitStatusSection
         sectionType="Changes to be committed:"
         files={stagedFilesDescriptions}