add default .arclint file

summary: add `.arclint` file now that lint engines are deprecated in global .arcconfig files.

auditors: csilvers, eater

Author: nsfmc

.arclint

@@ -0,0 +1,9 @@
+{
+  "linters": {
+    "khan-linter": {
+      "type": "script-and-regex",
+      "script-and-regex.script": "~\/khan\/devtools\/khan-linter\/runlint.py --always-exit-0 --blacklist=yes --propose-arc-fixes",
+      "script-and-regex.regex": "\/^((?P<file>[^:]*):(?P<line>\\d+):((?P<char>\\d+):)? (?P<name>((?P<error>E)|(?P<warning>W))\\S+) (?P<message>[^\\x00]*)(\\x00(?P<original>[^\\x00]*)\\x00(?P<replacement>[^\\x00]*)\\x00)?)|(?P<ignore>SKIPPING.*)$\/m"
+    }
+  }
+}