Bugs in Gazebo's README.md

[Agustin Alba Chicar]

1. There is a missing command at the build stage. We should add:

cd build

In between the mkdir build and the cmake step.

2. Where it says "cd {REPOSITORY_PATH}/terminus/docker" it should say "cd {REPOSITORY_PATH}/terminus-simulation/gazebo/docker".

3. Where it says "cd {REPOSITORY_PATH}/gazebo/docker" it should say "cd {REPOSITORY_PATH}/terminus-simulation/gazebo/docker"

4. Where it says "make gazebo-terminus-intel gazebo-terminus-intel" it should say "make gazebo8-terminus-intel gazebo8-terminus-intel"

[Agustin Alba Chicar]

Added some changes to the file as stated in the issue. Also modified some spelling mistakes. refs #167

→ <<cset 3c99ff6fde7f>>

[Agustin Alba Chicar]

Added one missing line. refs #167

→ <<cset dd707e2a1e69>>

[Agustin Alba Chicar]

Addressed some more spelling issues. refs #167

→ <<cset 9dae525b4546>>