revert order: install before source in local development flow

https://docs.conan.io/en/latest/developing_packages/package_dev_flow.html

If the ``conan install`` is not first, then the ``source`` might not have the settings defined, might fail because using the default profile instead of the one defined in ``conan install``

This needs to be swapped in the docs.

Open the package development flow page at docs.conan.io/en/latest/developing_packages/package_dev_flow.html and find the documented order of the conan install and source steps. Swap the order so conan install comes first, then verify the page explains that source uses the settings from that installation.

Written by the indexing model from the issue text.