Document Building From Source

[fkellner]

Please document how to build elm from source

Judging by the complexity of the old BuildFromSource.hs provided for 0.18 and older, how to build from source is not always totally obvious.

I had to ask the elm slack, and it seems like I'm not the only one having issues
(see e.g. #1892).

In the end, a custom stack.yaml and stack.build did it for me (Ubuntu 16.04, x86-64)

resolver: lts-13.27
projects:
   - '.'
extra-deps:
   - containers-0.5.11.0@sha256:28ad7337057442f75bc689315ab4ec7bdf5e6b2c39668f306672cecd82c02798
   - http-client-0.6.4@sha256:a74b417345857d4250bdb6d4ac7fd4a89fd2ad8efab3164c1a2b843398d5c13a
   - language-glsl-0.3.0@sha256:85c1e7bf2cf5d6e604b7a2899c27e2935033425944db200798e57849e64d4c81
   - network-2.6.3.6@sha256:1ca79d81af02d7acd6032d5e6c9bde4618a8fdcfbe19bd42b49d420183975df0
   - time-1.9.3@sha256:8f1b5448722a12a952248b356c9eb366e351226543d9086a2da71270522d5f45
   - binary-0.8.7.0@sha256:ae3e6cca723ac55c54bbb3fa771bcf18142bc727afd57818e66d6ee6c8044f12,7705
   - directory-1.3.4.0@sha256:500019f04494324d1df16cf83eefeb3f809b2b20b32a32ccd755ee0439c18bfd,2829
   - process-1.6.5.1@sha256:77a9afeb676357f67fe5cf1ad79aca0745fb6f7fb96b786d510af08f622643f6,2468
   - unix-2.7.2.2@sha256:e69269a17b9fa26cb77f3f55e86c39d0a4940ccfa0c4bc20826919d2572076ad,3496

(thanks to pd-andy and eh from the slack beginners channel!)

Also, there is a link loop:
If I follow the link under "Install" in the README.md, I get to the instructions from the documentation. If I follow the link to the npm package from there and go to troubleshooting (since my platform is not supported), when I follow "build from source" I get to the elm-platform repo which shows a link that it has moved here...

[fkellner]

Sorry, duplicate of #1894

[evancz]

This project prefers to have more new issues from more perspectives, so there is no need to close for "duplicates" here.

I added this to #1949 so it is recorded in a more organized way.