update contribution regarding new translatable strings

(Reverts commit ffc369d: "don't gitignore en.min.json file")

.gitignore

@@ -13,8 +13,7 @@ transifex.auth
 /dist/*.map
 /dist/data/
 /dist/img/*.svg
-/dist/locales/*.json
-!/dist/locales/en.min.json
+/dist/locales/en.min.json
 /dist/mapillary-js/
 /dist/pannellum/
 

CONTRIBUTING.md

@@ -277,11 +277,10 @@ only display them in the interface through the `t()` function.
 Then, add the new string to `data/core.yaml`. The translation system, Transifex,
 will automatically detect the change.
 
-If you are updating an existing string, update it in `data/core.yaml` and run
-`npm run build` to generate the `en.json` file automatically, then commit both
-modified files.
-
-Use `npm run build` to build the translations with the local changes.
+If you are adding or updating an existing string, update it in `data/core.yaml`
+and run `npm run build` to generate the `en.min.json` file automatically. Only
+commit the `data/core.yaml` file in your pull request. The translation system,
+Transifex, will automatically detect the changes.
 
 `npm run translations` can be used to pull the latest translations from Transifex.