docs: move AwsLambdaInstrumentor().instrument() to after the lambda function

[Kludex]

#2056 (comment)

tox -e docs doesn't work...

        File "/private/var/folders/q1/wn12m6td0tx0dy1s84xzrxbm0000gn/T/pip-install-nycnab7m/mysqlclient_22dcb881261f49e7b709df7ab13fc6ed/setup_posix.py", line 31, in mysql_config
          raise OSError("{} not found".format(_mysql_config_path))
      OSError: mysql_config not found
      [end of output]

[emdneto]

@Kludex I think tox—e docs needs some packages installed at the host level, like mysql_config. When running at CI, it works without any issue because it already has the package, so it's not a problem with the command itself.

[Kludex]

mysql_config

I got that, but where's the instruction?

[xrmx]

mysql_config

I got that, but where's the instruction?

It's one PR away!