Fix spelling of `ADITIONAL_VENV_PACKAGES`

This preserved `ADITIONAL_VENV_PACKAGES` as an input for backwards
compatiblity, but takes `ADDITIONAL_VENV_PACKAGES` with priority.

Fixes spelling in comment.

Related-Bug: #2046936
Change-Id: I84151d8f71b12da134e8fb9dbf3ae30f2a171fe2
diff --git a/stackrc b/stackrc
index 464e935..6cbadf9 100644
--- a/stackrc
+++ b/stackrc
@@ -207,8 +207,9 @@
 USE_VENV=$(trueorfalse False USE_VENV)
 
 # Add packages that need to be installed into a venv but are not in any
-# requirmenets files here, in a comma-separated list
-ADDITIONAL_VENV_PACKAGES=${ADITIONAL_VENV_PACKAGES:-""}
+# requirements files here, in a comma-separated list.
+# Currently only used when USE_VENV is true (individual project venvs)
+ADDITIONAL_VENV_PACKAGES=${ADDITIONAL_VENV_PACKAGES:-""}}
 
 # This can be used to turn database query logging on and off
 # (currently only implemented for MySQL backend)