Add caution notes on cache building (#1)

README.md

@@ -21,6 +21,7 @@ Offline Video Player is admittedly a specific solution to a specific problem, so
 
 - It only works with `.mp4` files
 - Changing any `.mp4` file in the `/videos` folder could disrupt the saved progress
+- Initial build of the cache can take from a few seconds **up to several minutes** depending on your machine and the number of videos; however, this should only happens once, the first time you run the app
 - Saved progress as well as cache is persisted as JSON files, no database involved
 - Being served locally, some best practices were skipped, i.e.: most operations are synchronous
 - Zero builds: frontend is not minified, backend only implements the basic CommonJS syntax

src/services/videos-cache.service.js

@@ -34,7 +34,7 @@ const build = async () => {
     `));
   }
 
-  log.write('Start building videos cache');
+  log.write('Start building videos cache (please wait)');
 
   const timeTaken = await asyncRecordTimeInSeconds(async () => {
     const files = getVideoPaths(paths.VIDEOS);