Docs: Minor edit to IR docs to mention longer intial/clean builds

  style="vertical-align:bottom;margin:0;"> and <strong>Debug</strong> <img src=

  "{@docRoot}images/tools/as-debugbutton.png" alt="" style=

  "vertical-align:bottom;margin:0;"> commands that significantly reduces the

  time between updates to your app. Instant Run pushes updates to your app

  without building a new APK, so changes are visible much more quickly.

  time between updates to your app. Although your first build may take longer

  to complete, Instant Run pushes subsequent updates to your app without

  building a new APK, so changes are visible much more quickly.

</p>

<p>