doc: massive refactor and simplification to migrate to mkdocs

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/config/limitations.md

@@ -0,0 +1,21 @@
+Limitations
+===========
+
+As of Finit v4 there are no limitations to where `.conf` settings can be
+placed.  Except for the system/global `rlimit` and `cgroup` top-level
+group declarations, which can only be set from `/etc/finit.conf`, since
+it is the first `.conf` file Finit reads.
+
+Originally, `/etc/finit.conf` was the only way to set up a Finit system.
+Today it is mainly used for bootstrap settings like system hostname,
+early module loading for watchdogd, network bringup and system shutdown.
+These can now also be set in any `.conf` file in `/etc/finit.d`.
+
+There is, however, nothing preventing you from having all configuration
+settings in `/etc/finit.conf`.
+
+> [!IMPORTANT]
+> The default `rcsd`, i.e., `/etc/finit.d`, was previously the Finit
+> [runparts](runparts.md) directory.  Finit >=v4.0 no longer has a
+> default `runparts` directory, make sure to update your setup, or the
+> finit configuration, accordingly.