rolldice: add page (tldr-pages#5811)

pages/linux/rolldice.md

@@ -0,0 +1,20 @@
+# rolldice
+
+> Roll virtual dice.
+> More information: <https://manned.org/rolldice>.
+
+- Roll a single 20 sided dice:
+
+`rolldice d{{20}}`
+
+- Roll two six sided dice and drop the lowest roll:
+
+`rolldice {{2}}d{{6}}s{{1}}`
+
+- Roll two 20 sided dice and add a modifier value:
+
+`rolldice {{2}}d{{20}}{{+5}}`
+
+- Roll a 20 sided dice two times:
+
+`rolldice {{2}}xd{{20}}`