misc/genreadme,tempfork/pkgdoc,tsnet: generate README.md files from godocbradtest

Adds a CI check and Makefile target to keep opted-in directories'
README.md files in sync with their package godoc. For now tsnet (and
its sub-packages under tsnet/example) is the only opted-in tree. The
list of directories lives in misc/genreadme/genreadme.go as
defaultRoots, so CI and humans both just run `make genreadme` with no
arguments.

The genreadme workflow runs `make genreadme` and fails if any
README.md is out of date, pointing the user at the same command.

Along the way:

 - tempfork/pkgdoc now emits Markdown instead of plain text: headings
   become level-2 with no {#hdr-...} anchors, and [Symbol] doc links
   resolve to pkg.go.dev URLs, including for symbols in the current
   package (which the default Printer would otherwise emit as bare
   #Name fragments with no backing anchor in a README). Parsing no
   longer uses parser.ImportsOnly, so doc.Package knows the package's
   symbols and can resolve [Symbol] links at all.

 - genreadme also emits a pkg.go.dev Go Reference badge at the top of
   a library package's README; suppressed for package main.

 - tsnet/tsnet.go's package godoc is expanded in idiomatic godoc
   syntax — [Type], [Type.Method], reference-style [link]: URL
   definitions — rather than Markdown-flavored [text](url) or
   backtick-quoted identifiers, so that both pkg.go.dev and the
   generated README.md render cleanly from a single source.

Fixes #19431
Fixes #19483
Fixes #19470

Change-Id: Iade21dc87921ab2bbb65951e5fb373b597fed29e
Signed-off-by: Walter Poupore <walterp@tailscale.com>

0 files changed, 0 insertions, 0 deletions