Update INSTALL.md: reminder to restart windows terminal

[jdeniau]

I tried to install gdu on windows, and got stuck after installation, because I needed to restart my terminal for Windows to handle gdu PATH.

I propose to add a single line that might help future Windows users.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.92%. Comparing base (836c39a) to head (bb2e5da).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #387      +/-   ##
==========================================
- Coverage   91.51%   90.92%   -0.60%     
==========================================
  Files          37       37              
  Lines        3242     3824     +582     
==========================================
+ Hits         2967     3477     +510     
- Misses        204      276      +72     
  Partials       71       71              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[dundee]

Thanks for your contribution!