Update to include instructions for checking out tags that addesses submodules

[steven-lai]

git clone --recursive https://github.com/VirusTotal/yara-python
cd yara-python
git checkout v3.10.0

This would cause yara-python to be at v3.10.0 but its submodule yara would stay at master (which currently happens to be v3.11.0). User should instead use: git checkout --recurse-submodules v3.10.0.

Documentation may want to include this information to prevent any confusion.