ffsend: add page (#2839)

pages/linux/ffsend.md

@@ -0,0 +1,24 @@
+# ffsend
+
+> Easily and securely share files from command line.
+> Homepage: <https://gitlab.com/timvisee/ffsend>.
+
+- Upload a file:
+
+`ffsend upload {{file}}`
+
+- Download a file:
+
+`ffsend download {{url}}`
+
+- Upload a file with password:
+
+`ffsend upload {{file}} -p {{password}}`
+
+- Download a file protected by password:
+
+`ffsend download {{file}} -p {{password}}`
+
+- Upload a file and allow 4 downloads:
+
+`ffsend upload {{file}} -d {{4}}`