docs: hint to yarn build before updating snapshots

MAINTAINERS.md

@@ -129,9 +129,9 @@ git commit -m 'chore: Update yarn.lock'
 ```
 
 It is safe to assume that any change to Endo will invalidate assumptions about
-guest application meters.
-Increment the meter type in `packages/xsnap/api.js`.
+guest application meters. 
 
+Increment the meter type in `packages/xsnap/api.js`:
 ```js
 export const METER_TYPE = 'xs-meter-0';
 ```
@@ -143,6 +143,11 @@ Endo changes nothing, bumping the meter version certainly will, and so
 predictably frustrates the kernel hash golden test.
 Update the test snapshots.
 
+```sh
+# at the repo root
+yarn build
+```
+
 ```sh
 cd packages/SwingSet
 yarn test test/test-xsnap-store.js --update-snapshots