Merge pull request #1690 from 25region/azdev-docs

Update az aro Python development documentation

docs/az-aro-python-development.md

@@ -60,6 +60,13 @@ Tests can be run as follows:
 azdev test aro (--live) (--lf) (--verbose) (--debug)
 ```
 
+> An issue was discovered on macOS when running tests due to additional security to restrict multithreading in macOS High Sierra and later versions of macOS. \
+If getting the following error:\
+`+[__NSCFConstantString initialize] may have been in progress in another thread when fork() was called.`\
+Add this variable to your env or add it to your profile to make it permanent in `~/.bash_profile` or `~/.zshrc`:\
+`export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES`
+
+
 There are two main types of tests:
 
 * live tests that get recorded and replayed