Update installation instructions

[rafmudaf]

Feature or improvement description
This pull request updates the installation instructions to add clarity and emphasize that compiling is only needed when changing the source code.

Related issue, if one exists
See the many issues where someone is compiling unnecessarily.

Impacted areas of the software
Installation documentation

Additional supporting information
Read this live at https://raf-openfast.readthedocs.io/en/docs-installation/source/install/index.html

[ebranlard]

I like the new binary section with the big warning for the DLLs

I think it would be valuable to start the "build from source" section with a quick start /TDLR.
Something like:

Here's the typical steps for each system, if you encounter problems, or are using a non-standard setup, please read the sections below.

For linux:

apt install xxx
git clone openfast  ; cd openfast
mkdir build ;  cd built  ; cmake ..
./glue-code/openfast/openfast -v

For mac:

brew install xxx
git clone openfast  ; cd openfast
mkdir build ;  cd built  ; cmake ..
./glue-code/openfast/openfast -v

For windows, different alternative are possible. if you have Visual studio, follow the instructions [here].

My favorite on windows is using msys2. Install msys2, open a sys2 shell (I'll probably need to double check):

pacman -Su base-devel git gcc g++ make mingw-w64-x86_64-lapack mingw-w64-x86_64-openblas  

Add the bin folder to you path ROOT_DIR\msys64\mingw64\bin; Then you can do the standard cmake approach

[rafmudaf]

@ebranlard I've added a list of general procedures for compiling. I'm avoiding duplicating information such as dependencies in order to avoid having to update multiple places in the documentation when this changes. I have the full commands for installing dependencies for Mac and linux already. Now in the beginning of the compiling section, there's something like checklist to follow.

[rafmudaf]

As for alternative methods for compiling, it's true that many other methods exist, but I also want to limit the amount of different methods that we support. Ideally, we would have one good pipeline for all systems, and we are actually quite close to that with CMake. In any case, once you have the msys procedure nailed down feel free to add a new section in the documentation describing it. We could add an "Other compiling methods" page or something along those lines. For example, with the new Intel tools (oneAPI) on Windows with CMake, I have to use the NMake Makefile generator rather than the VS generator in order for the Intel compiler to be found. This is a nuance that I would add in an "Others" section.

[ebranlard]

I still think that a linux and mac user would appreciate having all the commands to copy paste in a terminal readily available at the very top, as long as we have a big warning saying, read the documentation if it fails. For windows, it's a bit more tricky and for now we can tell the users to read the whole thing.