Copy over the documentation of the radix op from nqp.ops.

docs/ops.markdown

@@ -1,11 +1,11 @@
-# savecapture
+# savecapture()
 
 Gets hold of the argument capture passed to the current block.e
 Commits to doing enough copying that the list is valid any amount of time.
 See usecapture for a version of the op that doesn't promise that.
 Used by the multi-dispatcher.
 
-# usecapture
+# usecapture()
 
 Gets hold of the argument capture passed to the current block.
 (a future usecapture may invalidate it)
@@ -16,3 +16,19 @@ Used by the multi-dispatcher.
 
 Returns a hash containing the environment variables.
 Changing the hash doesn't affect the environment variables
+
+# radix($radix, $str, $pos, $flags)
+
+Convert string $str into a number starting at offset $pos and using radix $radix.
+The result of the conversion returns an array with
+    out[0] = converted value
+    out[1] = radix ** (number of digits converted)
+    out[2] = offset after consuming digits, -1 if no digits consumed
+The opcode skips single underscores between pairs of digits, per the Perl 6
+specification.
+
+The $flags is a bitmask that modifies the parse and/or result:
+    0x01: negate the result (useful if you've already parsed a minus)
+    0x02: parse a leading +/- and negate the result on -
+    0x04: parse trailing zeroes but do not include in result
+          (for parsing values after a decimal point)