update rpctransport docs

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (a7feb08) 41.55% compared to head (8ba5d70) 41.55%.

:exclamation: Current head 8ba5d70 differs from pull request most recent head 6ac2755. Consider uploading reports for the commit 6ac2755 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #224 +/- ## ======================================= Coverage 41.55% 41.55% ======================================= Files 17 17 Lines 746 746 Branches 131 131 ======================================= Hits 310 310 Misses 422 422 Partials 14 14 ``` | [Files Changed](https://app.codecov.io/gh/tatethurston/TwirpScript/pull/224?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tate+Thurston) | Coverage Δ | | |---|---|---| | [packages/twirpscript/src/runtime/client/index.ts](https://app.codecov.io/gh/tatethurston/TwirpScript/pull/224?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tate+Thurston#diff-cGFja2FnZXMvdHdpcnBzY3JpcHQvc3JjL3J1bnRpbWUvY2xpZW50L2luZGV4LnRz) | `92.98% <ø> (ø)` | | | [packages/twirpscript/src/node/index.ts](https://app.codecov.io/gh/tatethurston/TwirpScript/pull/224?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tate+Thurston#diff-cGFja2FnZXMvdHdpcnBzY3JpcHQvc3JjL25vZGUvaW5kZXgudHM=) | `100.00% <100.00%> (ø)` | |

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