Update install.md with GPG key addition via trusted.gpg.d and add ins…

…tructions to install Gazebo CMake from source

Signed-off-by: Trushant Adeshara <150821956+trushant05@users.noreply.github.com>

tutorials/install.md

@@ -21,7 +21,12 @@ sudo sh -c 'echo "deb http://packages.osrfoundation.org/gazebo/ubuntu-stable `ls
 
 Setup keys:
 ```
-wget http://packages.osrfoundation.org/gazebo.key -O - | sudo apt-key add -
+wget -qO - http://packages.osrfoundation.org/gazebo.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/gazebo-archive-keyring.gpg > /dev/null
+```
+
+You can check available version of libgz-tools using following command:
+```
+apt-cache search libgz-tools
 ```
 
 Install Gazebo Tools:
@@ -81,6 +86,14 @@ Gazebo Tools requires:
 
 * [Ruby](https://www.ruby-lang.org/). Refer to the [Ruby Documentation](https://www.ruby-lang.org/downloads/) for installation instructions. On Ubuntu systems `apt-get` can be used to install Ubuntu Package `ruby-dev`:
 
+Note: 
+In case the Gazebo CMake binary didn't work out for you, you can make it from source using following command:
+```
+echo "deb http://packages.osrfoundation.org/gazebo/ubuntu-stable `lsb_release -cs` main" > /etc/apt/sources.list.d/gazebo-stable.list
+sudo apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys D2486D2DD83DB69272AFE98867170598AF249743
+sudo apt update
+```
+
 ### Ubuntu Linux
 
 ```