pw_env_setup: Fix help string for argument
pw_env_setup: Fix help string for argument

Change-Id: I060b28dc735caabf018443d060d9f4bc45bbe290
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/24180
Pigweed-Auto-Submit: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>
Reviewed-by: Alexei Frolov <a1b001416a8cf9aaea32a3411f8f3c0793ebc0b5@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed