Adds a BCFtools-gcs installer doc

[MattWellie]

Context: I'm setting up a fresh laptop, and while this repo should contain a baby steps setup guide for core tools, it seems more focused on setting up a terminal with a RAD colour scheme. I'm planning to add help pages describing from-zero setup in more detail than this repo currently contains. This is a first page covering the steps I've needed for bcftools-gcs-gcloud to all play nicely on a new Mac.

Adds a step-by-step installation process for bcftools, configured for interacting with GCS. These steps broadly follow the standard installation steps here, but with some extra details:

• assuming this is part of early setup on a CPG-issued laptop, XCode + license agreement is required to 'activate' gcc
• the MacOS bundled libcurl didn't play well with me, spitting out endless libcurl_open...Retrying error messages; unsure if I'm very unlucky, or if this is a general issue. The fix described here solved this for me, but I had a working install on my previous laptop and I don't remember requiring these steps. Though.. I did have a non-standard curl on that laptop... maybe it was installed outside of homebrew to the same effect

[EddieLF]

Looks good, glad to add some proper docs for this. A few small notes

1. Is it worth expanding this to include samtools commands as well? AFAIK the GCS connecting aspect is identical and most commands are similar.

2. Might be worth mentioning that you should already have gcloud installed and authed, and maybe a note on access policies for data in buckets - i.e. you will need the right permissions or a PAM approval to access -main bucket files. There are some "instructions" for gcloud install and auth here and for data access here.

3. I think we can export the GCS_OAUTH_TOKEN variable to our environment and then drop it from the commands.
   I've always begun my samtools and bcftools commands with GCS_OAUTH_TOKEN=$(gcloud auth application-default print-access-token) ..., but this comment on a biostars forum post shows you can export the env variable and then it will just work. So it might be good to add that you can stick export GCS_OAUTH_TOKEN=$(gcloud auth print-access-token) into your .zshrc

[MattWellie]

Adding samtools to this is a good idea, I'll shove that in too.

I'm planning to also make a from-zero page on gcloud setup, and once that exists this can link to that.

exporting it makes sense, tidies things up. I'll expand this page by being more explicit that GCS_OAUTH_TOKEN is required by BCFtools, and it can either be done in-line, or with a helper

[MattWellie]

Alright, maybe this problem is somehow unique to me... the brew-installed version may or may not work just fine 🫠