refactor(swap): rename imported .md files to md- prefix for swap mechanism

Restore the canary file naming convention that swap_sources.py expects:
the imported MyST pages now live as docs/<dir>/md-<name>.md alongside
the existing docs/<dir>/<name>.rst, so swap_sources.py --swap can rename
them into place at build time.

- 254 .md files renamed (every page with a matching .rst counterpart)
- 2 MyST-only pages left at their final names (no .rst exists, no swap
  needed): docs/copyright.md, docs/automation/terraform/terraformvyos.md

All 114 stems listed in docs/_swap.txt now have a corresponding
md-<name>.md source file ready to swap in.

🤖 Generated by [robots](https://vyos.io)

1 files changed, 21 insertions, 0 deletions

diff --git a/docs/introducing/md-about.md b/docs/introducing/md-about.md
new file mode 100644
index 00000000..ec4ff30d
--- /dev/null
+++ b/docs/introducing/md-about.md
@@ -0,0 +1,21 @@
+(about)=
+
+# About
+
+VyOS is an open-source network operating system that provides a single unified
+CLI and API to manage routing protocols, firewall and NAT, QoS, load balancing,
+DHCP and DNS servers, and many other features.
+
+VyOS runs on a wide variety of commodity hardware, virtual machines, and
+multiple cloud environments.
+
+We provide a dedicated user guide for each major
+VyOS release that receives long-term support (LTS). We maintain multiple user
+guide versions, all hosted at <https://docs.vyos.io>.
+To switch between versions, select the appropriate version in the bottom-right
+corner.
+
+VyOS CLI syntax may vary between major and sometimes minor releases. Always
+refer to the documentation matching your current running installation. If
+a change in the CLI is required, VyOS provides a migration script to handle
+the syntax adjustments. No user action is required.