Update FAQ for Upcoming GDC Data Release

[jamesqo]

Updates the cBioPortal FAQ to address the points in knowledgesystems/pipelines-scrum#1352, including:

• Genome Build (Hg38?)
• ASCAT vs GISTIC Copy Number
• How GDC data differs from PanCan
• Used mutation callers, it it union or some? [not sure what is meant by this?]
• GDC Data availability/difference from existing cBioPortal data

Checks

• The commit log is comprehensible. It follows 7 rules of great commit messages. We can fix this during merge by using a squash+merge if necessary
• Has tests or has a separate issue that describes the types of test that should be created. If no test is included it should explicitly be mentioned in the PR why there is no test.
• Is this PR adding logic based on one or more clinical attributes? If yes, please make sure validation for this attribute is also present in the data validation / data loading layers (in backend repo) and documented in File-Formats Clinical data section!
• Make sure your PR has one of the labels defined in https://github.com/cBioPortal/cbioportal/blob/master/.github/release-drafter.yml

Any screenshots or GIFs?

If this is a new visual feature please add a before/after screenshot or gif
here with e.g. Giphy CAPTURE or Peek

Notify reviewers

/cc @inodb @tmazor @schultzn @averyniceday @ritikakundra @n1zea144

[n1zea144]

I think we need to have a discussion about the content in the TCGA section.

[inodb]

LGTM! Left a few comments

[tmazor]

Looks good overall - just one main suggestion to combine two Qs into a single 'what are all these different TCGA studies?' type question.

[sonarcloud]

Quality Gate passed

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