README updates on requirements for erl -man?

[bklebe]

The default kerl doc target is now chunks, which doesn't install the PDF, HTML, or manpage docs: https://github.com/kerl/kerl#kerl_doc_targets. Thus erl -man doesn't work by default. I'd like to write a PR to fix the README on this note but I'm not quite sure how to word this change. I found that I could only get them to install when setting KERL_DOC_TARGETS="man chunks" explicitly.

[Stratus3D]

Hi @bklebe , thanks for bringing this up. I'm not certain how this fits with the KERL_BUILD_DOCS, KERL_INSTALL_HTMLDOCS, and KERL_INSTALL_MANPAGES environment variables we have documented in the asdf-erlang readme.

You are welcome to take a stab at updating the Getting Erlang documentation section of the readme.