Add restart/reload note about env variables

Fixes #10450

Author: tannewt

docs/environment.rst

@@ -53,8 +53,9 @@ Details of the toml language subset
 CircuitPython behavior
 ----------------------
 
-CircuitPython will also read the environment to configure its behavior. Other
-keys are ignored by CircuitPython. Here are the keys it uses:
+CircuitPython will also read the environment to configure its behavior. Some keys are read at
+startup once and others are read on reload. If a reload doesn't change things, then try a restart.
+Other keys are ignored by CircuitPython. Here are the keys it uses:
 
 Core CircuitPython keys
 ^^^^^^^^^^^^^^^^^^^^^^^