Rewrite onboarding prose to a neutral voice

tests/test_doctor.sh

@@ -15,8 +15,8 @@ out="$(mktemp)"
 trap 'rm -f "$out"' EXIT
 
 # Strip everything that could satisfy the checks we want to fail.
-# /usr/bin/python3 is 3.10.x on Ubuntu 22.04; that's fine: we want to
-# prove the python>=3.11 miss branch renders its fix+alt lines.
+# /usr/bin/python3 is 3.10.x on Ubuntu 22.04; this case exercises the
+# python>=3.11 miss branch and its fix+alt lines.
 if env -i HOME="$HOME" PATH="/usr/bin:/bin" bash "$repo/scripts/doctor.sh" >"$out" 2>&1; then
     echo "FAIL: doctor.sh exited 0 despite missing prerequisites"
     cat "$out"