docs: quick start go get leaves the module unbuildable

[tonydzi]

What was broken

docs/quick_start.md → Installation says:

go get github.com/modelcontextprotocol/go-sdk

The module root holds no importable package (only copyright_test.go), so go get on the
module path records the requirement as // indirect and writes none of the go.sum entries
the mcp package needs. A reader who runs that command and then pastes the server snippet
from the next section hits six errors on the first build — before writing a line of their own.

How I checked

Followed the page verbatim on Go 1.26.4, in an empty directory:

$ go mod init example.com/qs
$ go get github.com/modelcontextprotocol/go-sdk
go: added github.com/modelcontextprotocol/go-sdk v1.7.0

go.mod now reads require github.com/modelcontextprotocol/go-sdk v1.7.0 // indirect.
Then the two snippets from Getting started, saved as server/main.go and client/main.go:

$ go build ./...
missing go.sum entry for module providing package github.com/google/jsonschema-go/jsonschema (imported by github.com/modelcontextprotocol/go-sdk/mcp)
missing go.sum entry for module providing package golang.org/x/oauth2 (imported by github.com/modelcontextprotocol/go-sdk/mcp)
missing go.sum entry for module providing package github.com/segmentio/encoding/json (imported by github.com/modelcontextprotocol/go-sdk/internal/json)
missing go.sum entry for module providing package github.com/yosida95/uritemplate/v3 (imported by github.com/modelcontextprotocol/go-sdk/mcp)
missing go.sum entry for module providing package golang.org/x/sync/errgroup (imported by github.com/modelcontextprotocol/go-sdk/mcp)
missing go.sum entry for module providing package golang.org/x/time/rate (imported by github.com/modelcontextprotocol/go-sdk/mcp)

Same directory, same snippets, asking for the package instead:

$ go get github.com/modelcontextprotocol/go-sdk/mcp
$ go build -o myserver ./server && go build -o myclient ./client
$ ./myclient
{"greeting":"Hi you"}

go mod tidy after the fact fixes it too — that is the escape hatch the note mentions,
but it is not what the page tells you to do.

What it is now

go get github.com/modelcontextprotocol/go-sdk/mcp

plus four lines saying why the module path alone is not enough, so the next person who
copies the module path from go.mod or from a search result knows what they are looking at.

Change is in internal/docs/quick_start.src.md; docs/quick_start.md regenerated with
go generate ./internal/docs, both committed together. Docs-only, no code paths touched.

---

Assisted-by: Claude Opus 5 — this PR was drafted and verified by Anton's AI cofounder running
on his account; every command and output above is from a real run on this machine, not a
reconstruction.

[guglielmo-san]

let's remove this comment

[tonydzi]

Done — dropped the paragraph, the PR is now just the one-line go get fix in both the source and the generated doc. Thanks for the quick look.

[guglielmo-san]

Thanks for the contribution!