Clarify "Starting as a Contributor" document

[Seb]

On Monday, 11 December 2017 at 14:13:41 UTC, Dukc wrote:
> On Sunday, 10 December 2017 at 08:18:17 UTC, Ali Çehreli wrote:
>> This page is very good:
>>
>>   https://wiki.dlang.org/Starting_as_a_Contributor
>>
>> I need clarifications
>
> Another oddity: Someone has apparently made DRuntime build to 
> use ../dmd/generated/windows/32/dmd instead of the "system" dmd 
> recently. Perhaps the idea here is that I do not have to go 
> replacing my system dmd anymore.

Yes, that someone would be myself.

https://github.com/dlang/druntime/pull/1978

It's part of a long-lasting effort to get rid of `src/dmd`,
s.t. we can rename the `ddmd` package to `dmd`.
See:

https://github.com/dlang/dmd/pull/7135

> But the problem is that when I build dmd, for some reason, the 
> build file deletes that generated dmd at the end. Can be 
> resolved by moving the dmd manually to that directory, but that 
> is not explained at the web page. Should we tweak dmd to build 
> into the generated directory instead of working directory, or 
> tweak DRuntime to use ../dmd/src/dmd instead? Or am I missing 
> something?

As explained, it's a huge effort to switch from ../src/dmd to to 
../generated, because in the meantime none of the existing CIs 
and integrations etc. are allowed to break.
However, it sounds weird that the generated dmd executable get 
removed.
How do you build dmd and what are your system details?