Fixed small typo in navigation_py docs: pythong->python

[ivrolan]

Main Changes

Fixes #335 changing changing .with_build_pythong_bindings() to .with_build_python_bindings() as explained below:

In the python example for navigation, the proposed codeblock for the use of the functions using the Direct Interface, there is a note that says

# Note: to use the direct interface you need to build using
#       .with_build_pythong_bindings()
import sys
....

However, this does not exist. I supposed it was a small spelling mistake and I fixed in this PR to:

# Note: to use the direct interface you need to build using
#       .with_build_python_bindings()
import sys
....

[alphaville]

Many thanks for spotting this typo!