Explain "self time" in graph view (jaegertracing#655)

Signed-off-by: Yuri Shkuro <github@ysh.us>
Signed-off-by: vvvprabhakar <vvvprabhakar@gmail.com>

packages/jaeger-ui/src/components/TracePage/TraceGraph/TraceGraph.tsx

@@ -82,7 +82,7 @@ const HELP_CONTENT = (
               </Button>
             </td>
             <td>Selftime</td>
-            <td>Colored by self time</td>
+            <td>Colored by self time (*)</td>
           </tr>
         </tbody>
       </table>
@@ -105,6 +105,10 @@ const HELP_CONTENT = (
         </text>
       </svg>
     </div>
+    <div>
+      (*) <b>Self time</b> is the total time spent in a span when it was not waiting on children. For example,
+      a 10ms span with two 4ms non-overlapping children would have <b>self-time = 10ms - 2 * 4ms = 2ms</b>.
+    </div>
   </div>
 );