Document Nightscout database size info row and alarm (#46)

* Document Nightscout database size info row and alarm

Add the DB Size info row to the Information Display table and the
Nightscout Database Size alarm to the Alarm Types reference, with a note
explaining the dbsize plugin requirement and the DBSIZE_MAX caveat.

* Clarify DB Size description in lf-setup.md

Updated the DB Size description to specify Megabytes (MB) instead of MiB for clarity.

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Co-authored-by: Marion Barker <19607791+marionbarker@users.noreply.github.com>

Author: bjorkert

docs/setup/lf-features.md

@@ -75,6 +75,7 @@ The table below lists every alarm type available in *LoopFollow*, organized by g
 | Sensor Change Alert | Sensor change due |
 | Not Looping Alert | Loop hasn't completed within a configurable number of minutes |
 | Looping app expiration | Looping-app build is expiring soon |
+| Nightscout Database Size | *Nightscout* database has filled to or above a chosen percentage of its configured size limit (defaults to 75%, daytime only) |
 
 #### Override / Target
 

docs/setup/lf-setup.md

@@ -265,6 +265,10 @@ These items can be chosen for display on the Home screen. A Nightscout Site is r
 | Updated | Time of last `loop` | `Trio` |
 | TDD | Total Daily Dose in the last 24 hours | `Trio` |
 | IAGE | Insulin Age | Both |
+| DB Size | *Nightscout* database size: Megabytes (MB) used and the percentage of the site's configured limit. Hidden by default | Both |
+
+!!! note "DB Size"
+    The **DB Size** row and the [*Nightscout* Database Size alarm](lf-features.md#alarms){: target="_blank" } both read from *Nightscout*'s `dbsize` plugin, so your site must have that plugin enabled. The percentage is measured against the site's `DBSIZE_MAX` setting, which is **496 MB** unless the site owner changed it. Because that setting may not match your hosting plan's real limit, the row leads with the absolute used MB figure, which is always meaningful.
 
 ### Units and Metrics