added a tip to keep the preview window floating

 README.md | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/README.md b/README.md
index cb8268c..940dee2 100644
--- a/README.md
+++ b/README.md
@@ -93,3 +93,10 @@ export FONTPREVIEW_FG_COLOR="#000000"
 
 # Preview text that should be displayed in the font preview window
 export FONTPREVIEW_PREVIEW_TEXT="ABCDEFGHIJKLM\nNOPQRSTUVWXYZ\nabcdefghijklm\nnopqrstuvwxyz\n1234567890\n!@$\%(){}[]"
+```
+
+## Tips
+It is recommended to have the preview window floating. So if you use i3wm or a variant, put this in your config:
+```
+for_window [instance="fontpreview"] floating enable
+```