docs: include StreamType enum description in new docs

[RanAwaySuccessfully]

Please describe the changes this PR makes and why it should be merged:

https://discord.js.org/#/docs/voice/stable/typedef/StreamType

The link above does not have a description for the StreamType enum. This pull request should hopefully include them.

Status and versioning classification:

• This PR only includes non-code changes, like changes to documentation, README, etc.
• Code changes have been tested against the Discord API, or there are no code changes

[codecov[bot]]

Codecov Report

Merging #239 (d3a3e45) into stable (3dabc30) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           stable     #239   +/-   ##
=======================================
  Coverage   73.65%   73.65%           
=======================================
  Files          21       21           
  Lines         911      911           
  Branches      227      221    -6     
=======================================
  Hits          671      671           
  Misses        238      238           
  Partials        2        2           

Impacted Files	Coverage Δ
src/audio/TransformerGraph.ts	77.96% <ø> (ø)

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