Add long descriptions to some plugins

Edited the short descriptions to answer the question
"What can I do with this extension" to help users decide
whether they need it.

In long descriptions, tell users what else they need to
be able to use the plugin.

Change-Id: Iefce7505b61fc77cf38cc915f1f7dbd25c9cb570
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/CMakeProjectManager.json.in

@@ -13,7 +13,13 @@
                   "Alternatively, this plugin may be used under the terms of the GNU General Public License version 3 as published by the Free Software Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT included in the packaging of this plugin. Please review the following information to ensure the GNU General Public License requirements will be met: https://www.gnu.org/licenses/gpl-3.0.html."
     ],
     "Category" : "Build Systems",
-    "Description" : "CMake support.",
+    "Description" : "Automate the configuration of build systems with CMake",
+    "LongDescription" : [
+        "CMake controls the software compilation process by using simple configuration files, called CMakeLists.txt files."
+        "You also need:",
+            "- CMake",
+        "Qt Online Installer installs a CMake version that you can use."
+    ],
     "Url" : "https://www.qt.io",
     ${IDE_PLUGIN_DEPENDENCIES},