"Install dependencies" needs additional command line options

TS and JS Grammar Extension version: 0.0.50 / latest

In README.md, it is documented that to install dependencies, npm install is all that is required. However, I've found that on my Windows 10 machine with Visual Studio 2017, I have to type npm install -g windows-build-tools in a PowerShell running with administrator privileges or oniguruma fails to be installed.

It appears that after I get it to build one time, I don't have to pass those extra arguments to npm.

I found my solution when someone else had a similar problem on superuser.com. I'm logging this here to help others having the same problem, and as a suggestion that the README.md be updated to include the extra arguments needed on Windows 10.

Actualiza las instrucciones de instalación de dependencias de README.md para el caso reportado en Windows 10. Empieza revisando las indicaciones existentes sobre npm install y el fallo de oniguruma descrito en el issue; se considera terminado cuando el README documente claramente el comando adicional de PowerShell con privilegios de administrador y cuándo es necesario.