Update README.md (#2124)

* Update README.md

Signed-off-by: Alejandro Hernández Cordero <ahcorde@gmail.com>

* Update README.md

Co-authored-by: Ian Chen <ichen@openrobotics.org>
Signed-off-by: Michael Carroll <carroll.michael@gmail.com>

---------

Signed-off-by: Alejandro Hernández Cordero <ahcorde@gmail.com>
Signed-off-by: Michael Carroll <carroll.michael@gmail.com>
Co-authored-by: Michael Carroll <mjcarroll@intrinsic.ai>
Co-authored-by: Ian Chen <ichen@openrobotics.org>

README.md

@@ -78,7 +78,7 @@ introspection and control.
 
 # Install
 
-See the [installation tutorial](https://gazebosim.org/api/gazebo/6.1/install.html).
+See the [installation tutorial](https://gazebosim.org/api/sim/8/install.html).
 
 # Usage
 
@@ -125,11 +125,11 @@ This issue is tracked [here](https://github.com/gazebosim/gz-tools/issues/8).
 
 # Documentation
 
-See the [installation tutorial](https://gazebosim.org/api/gazebo/6.1/install.html).
+See the [installation tutorial](https://gazebosim.org/api/sim/8/install.html).
 
 # Testing
 
-See the [installation tutorial](https://gazebosim.org/api/gazebo/6.1/install.html).
+See the [installation tutorial](https://gazebosim.org/api/sim/8/install.html).
 
 See the [Writing Tests section of the contributor guide](https://github.com/gazebosim/gz-sim/blob/main/CONTRIBUTING.md#writing-tests) for help creating or modifying tests.
 
@@ -145,6 +145,7 @@ gz-sim
 │   └── worlds                   Example SDF world files.
 ├── include/gz/sim               Header files that downstream users are expected to use.
 │   └── detail                   Header files that are not intended for downstream use, mainly template implementations.
+├── python                       Python wrappers
 ├── src                          Source files and unit tests.
 │   ├── gui                      Graphical interface source code.
 │   └── systems                  System source code.