Add tasks for all the new languages

Task/Self-describing-numbers/Nim/self-describing-numbers.nim

@@ -0,0 +1,20 @@
+import strutils
+
+proc count(s, sub): int =
+  var i = 0
+  while true:
+    i = s.find(sub, i)
+    if i < 0:
+      break
+    inc i
+    inc result
+
+proc isSelfDescribing(n): bool =
+  let s = $n
+  for i, ch in s:
+    if s.count($i) != parseInt("" & ch):
+      return false
+  return true
+
+for x in 0 .. 4_000_000:
+  if isSelfDescribing(x): echo x