Echo info about steps in generated env setup script.
Also run 'pw doctor' at end of env setup script.
Non-warning/error output can be suppressed by setting
PW_ENVSETUP_QUIET to '1'.
Change-Id: Ief333779dabbdb4613db05726d00f80d3fca325a
Add 'pw doctor' command to check environment is correctly set up
for pigweed. For now contains minimal checks.
Change-Id: Icb132c89bb272b52c57dae0451b24966b48d4e90
Bug: 28