docs(readme): wrap pre-existing long lines for MyST doc-lint

The doc-linter was extended to MyST .md files in 7a3aa29 (after the
previous README refresh in 3a544f6), so this PR is the first README
edit linted under MyST rules. The three pre-existing >80-char lines
(badge, Wayback link, rolling table row) now fail doc-lint. Wrap them:

- Switch the badge and Wayback links to reference-style. The badge
  destination/image URLs become [badge]/[rtd]/[wayback] references at
  the top of the file; renders identically on GitHub and in Sphinx.
- Trim the Wayback snapshot path from web/20200225171529/ to web/2020/
  (year-level capture, same era as the original snapshot) to fit the
  reference definition in 80 chars without a suppression marker. Using
  % stop_vyoslinter here would render literally on GitHub, since the
  README is GFM-rendered, not MyST.
- Shorten the rolling-branch table row from 'all new contributions
  target this' to 'new contributions land here' (84 -> 78 chars).

Also address two Copilot review findings on this PR:

- Line 15 grammar: 'Pages are ... and build with Sphinx' ->
  'Pages are ... and are built with Sphinx'.
- AGENTS.md still describes the source format as mixed MyST/RST
  (AGENTS.md:7 and several follow-up sections). Updating AGENTS.md
  in this PR would pull ~30 pre-existing long-line violations into
  scope and require a bulk hard-wrap of the file, which is outside
  the original README request. Leaving AGENTS.md for a follow-up PR
  and noting it in the PR description.

1 files changed, 8 insertions, 4 deletions

diff --git a/README.md b/README.md
index 17ddf8a6..a1364b36 100644
--- a/README.md
+++ b/README.md
@@ -3,15 +3,19 @@
 Source for the VyOS user documentation hosted on Read the Docs at
 https://docs.vyos.io.
 
-[![Documentation Status](https://readthedocs.org/projects/vyos/badge/?version=rolling)](https://docs.vyos.io/en/rolling/?badge=rolling)
+[![Documentation Status][badge]][rtd]
 
 The earlier wiki for VyOS 1.1.x and pre-1.2.0 docs is preserved on the
-[Wayback Machine](https://web.archive.org/web/20200225171529/https://wiki.vyos.net/wiki/Main_Page).
+[Wayback Machine][wayback].
+
+[badge]: https://readthedocs.org/projects/vyos/badge/?version=rolling
+[rtd]: https://docs.vyos.io/en/rolling/?badge=rolling
+[wayback]: https://web.archive.org/web/2020/https://wiki.vyos.net/wiki/Main_Page
 
 ## Source format
 
 Pages are [MyST Markdown](https://myst-parser.readthedocs.io/) (`.md`) and
-build with Sphinx — `source_suffix` in `docs/conf.py` lists `.md` only.
+are built with Sphinx — `source_suffix` in `docs/conf.py` lists `.md` only.
 The pre-migration RST originals are archived under `docs/_rst_legacy/`
 for reference; they are excluded from the build and should not be edited.
 
@@ -29,7 +33,7 @@ constellation:
 
 | Branch | VyOS version | Role |
 |--------|--------------|------|
-| `rolling` | 1.5+ rolling | Default branch — all new contributions target this. |
+| `rolling` | 1.5+ rolling | Default branch — new contributions land here. |
 | `circinus` | 1.5.x | LTS docs. |
 | `sagitta` | 1.4.x | Previous LTS docs. |
 | `equuleus` | 1.3.x | Legacy. |