Default location for config file lost.

[TonyB9000]

Former behavior was to seek the config file under "(user)/.esg/esg.yaml" (actually, esg.ini). Now it requires explicit "--config" path.
We should either support the original path search, or explain in the help-text that it is no longer supported.

[sashakames]

Thanks, we should support it on linux, macox, etc. but may not work on windows if $HOME does not exist, ie. os.environ["HOME"]

[sashakames]

Just tested and perhaps just a typo prevented it from working. Staged for next release: v5.2.3