Table: Add example for selectable rows

[mcarrano]

In the Table component we should show as example of a table with selectable rows. We currently have this example that illustrates use of a Row Click Handler (https://www.patternfly.org/v4/components/table#row-click-handler-and-header-cell-tooltipspopovers) but it doesn't show the corresponding styles for selectable rows that were added per this core PR: patternfly/patternfly#3835

cc @mcoker

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patternfly/patternfly#3835 adds:

• .pf-m-hoverable - this class can be added to either a <tr> for a non-expandable individual table row or a <tbody> for an expandable row.
  • those elements need tabindex="0" so they can be interacted with via keyboard.
• .pf-m-selected to the same elements for when the row or expandable row is in the selected state.