doc(lock): add lockfile doc with customization explanation

docs/pages/_meta.json

@@ -3,6 +3,7 @@
   "quick": "Quick Start",
   "installation": "Installation",
   "config": "Configuration",
+  "lockfile": "Lockfile",
   "location": "Locations",
   "backend": "Backend",
   "cli": "CLI",

docs/pages/cli/general.md

@@ -37,7 +37,7 @@ autorestic --restic-bin /some/path/to/my/custom/restic/binary
 
 ## `--lockfile-path`
 
-Specify the path for the lockfile used by `autorestic`. If omitted, this will default to `.autorestic.lock.yml` next to the loaded config file.
+Specify the path for the [lockfile](../lockfile.md) used by `autorestic`. If omitted, this will default to `.autorestic.lock.yml` next to the loaded config file.
 
 ```bash
 autorestic --lockfile-path /path/to/my/.autorestic.lock.yml

docs/pages/lockfile.md

@@ -0,0 +1,14 @@
+# Lockfile
+
+Under the hood, `autorestic` uses a lockfile to ensure that only one instance is running and to keep track of when [cronjobs](./location/cron.md) were last run.
+
+By default, the lockfile is stored next to your [configuration file](./config.md) as `.autorestic.lock.yml`. In other words, if your config file is located at `/some/path/.autorestic.yml`, then the lockfile will be located at `/some/path/.autorestic.lock.yml`.
+
+## Customization
+
+The path to the lockfile can be customized if need be. This can be done is a few ways:
+
+1. Using the `--lockfile-path ...` command line flag
+1. Setting `lockfile: ...` in the configuration file
+
+Note that `autorestic` will check for a customized lockfile path in the order listed above. This means that if you specify a lockfile path in multiple places, the method that's higher in the list will win.