Add instruction to resolve the inotify watch limit issue

On Linux, it's common that the system limit the number of files that can be monitored. If
this limit is too low then the build script will fail.

Signed-off-by: Danny Colin <contact@dannycolin.com>

README.md

@@ -288,6 +288,7 @@ yarn install
 yarn start
 ```
 
+
 Wait a few seconds for the initial build to finish; you should see something like:
 ```
 Hash: b0af76309dd56d7275c8
@@ -309,6 +310,23 @@ modifying it. See the [configuration docs](docs/config.md) for details.
 
 Open http://127.0.0.1:8080/ in your browser to see your newly built Riot.
 
+**Note**: The build script uses inotify by default on Linux to monitor directories 
+for changes. If the inotify watch limit is too low your build will silently fail.
+To avoid this issue, we recommend a limit of at least 128M.
+
+To set a new inotify watch limit, execute:
+
+```
+$ sudo sysctl fs.inotify.max_user_watches=131072
+$ sudo sysctl -p
+```
+
+If you wish, you can make this new limit permanent, by executing:
+
+```
+$ echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf
+$ sudo sysctl -p
+```
 ___
 
 When you make changes to `matrix-react-sdk` or `matrix-js-sdk` they should be