chore(markdown): Updated plugin docs

markdown/dev/reference/plugins/measurements/en.md

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+---
+title: "@freesewing/plugin-measurements"
+---
+
+The **@freesewing/plugin-measurements** plugin attaches
+to [the preDraft lifecycle hook](/reference/api/hooks/predraft) to
+provide a number of extra measurements to your pattern insofar as
+they can be deduced from the measurements that are provided.
+
+It will add the following measurements:
+
+ - `seatFront` (if both `seat` and `seatBack` are provided)
+ - `seatBackArc` (if both `seat` and `seatBack` are provided) 
+ - `seatFrontArc` (if both `seat` and `seatBack` are provided)
+ - `waistFront` (if both `waist` and `waistBack` are provided)
+ - `waistBackArc` (if both `waist` and `waistBack` are provided) 
+ - `waistFrontArc` (if both `waist` and `waistBack` are provided)
+ - `crossSeamBack` (if both `crossSeam` and `crossSeamFront` are available)
+
+## Installation
+
+```sh
+npm install @freesewing/plugin-measurements
+```
+
+## Usage
+
+Like all [build-time plugins](/guides/plugins/types-of-plugins#build-time-plugins), you
+load them by passing them to the [freesewing.Design](/reference/api/design) super-constructor:
+
+```js
+import freesewing from "@freesewing/core";
+import measurements from "@freesewing/plugin-measurements";
+import config from "../config";
+
+const Pattern = new freesewing.Design(config, measurements);
+```
+