i.landsat.download manual: update to new product names (#451)

* i.landsat.download manual: update to new product names

* Use table for readability

Table borrowed from https://github.com/yannforget/landsatxplore/blob/master/README.md

grass7/imagery/i.landsat/i.landsat.download/i.landsat.download.html

@@ -3,9 +3,57 @@ <h2>DESCRIPTION</h2>
 <em>i.landsat.download</em> allows to search and download Landsat TM, ETM and OLI data
 from USGS <a href="https://earthexplorer.usgs.gov/">EarthExplorer</a> through
 the <a href="https://github.com/yannforget/landsatxplore">landsatxplore</a>
-Python library. Datasets currently supported include: Landsat 5 TM (LANDSAT_TM_C1),
-Landsat 7 ETM (LANDSAT_ETM_C1) and Landsat 8 OLI (LANDSAT_8_C1) from
-<a href="https://www.usgs.gov/core-science-systems/nli/landsat/landsat-collection-1?qt-science_support_page_related_con=1#qt-science_support_page_related_con">Collection 1</a>.
+Python library. Datasets currently supported include
+<a href="https://www.usgs.gov/core-science-systems/nli/landsat/landsat-collection-1?qt-science_support_page_related_con=1#qt-science_support_page_related_con">Collection 1</a>
+and 
+<a href="https://www.usgs.gov/core-science-systems/nli/landsat/landsat-collection-2?qt-science_support_page_related_con=2#qt-science_support_page_related_con">Collection 2</a>.
+
+<table>
+<thead>
+<tr>
+<th>Dataset Name</th>
+<th>Dataset ID</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>Landsat 5 TM Collection 1 Level 1</td>
+<td><code>landsat_tm_c1</code></td>
+</tr>
+<tr>
+<td>Landsat 5 TM Collection 2 Level 1</td>
+<td><code>landsat_tm_c2_l1</code></td>
+</tr>
+<tr>
+<td>Landsat 5 TM Collection 2 Level 2</td>
+<td><code>landsat_tm_c2_l2</code></td>
+</tr>
+<tr>
+<td>Landsat 7 ETM+ Collection 1 Level 1</td>
+<td><code>landsat_etm_c1</code></td>
+</tr>
+<tr>
+<td>Landsat 7 ETM+ Collection 2 Level 1</td>
+<td><code>landsat_etm_c2_l1</code></td>
+</tr>
+<tr>
+<td>Landsat 7 ETM+ Collection 2 Level 2</td>
+<td><code>landsat_etm_c2_l2</code></td>
+</tr>
+<tr>
+<td>Landsat 8 Collection 1 Level 1</td>
+<td><code>landsat_8_c1</code></td>
+</tr>
+<tr>
+<td>Landsat 8 Collection 2 Level 1</td>
+<td><code>landsat_ot_c2_l1</code></td>
+</tr>
+<tr>
+<td>Landsat 8 Collection 2 Level 2</td>
+<td><code>landsat_ot_c2_l2</code></td>
+</tr>
+</tbody>
+</table>
 
 <p>
 To connect to EarthExplorer both a <em>user</em> name and <em>password</em>