Adds a gotcha regarding Less and @ rules to address issue #197

When using Less there needs to be a mixin to escape the @ rules. This
adds some simple documentation for it.

README.md

@@ -755,6 +755,15 @@ div {
 - If you're using [Less](http://lesscss.org/) there are sometimes issues with fractions being divided before Lost can interpret them.
   - To fix, escape the math like so: `lost-column: ~"1/2";`.
   - See: [Lost issue 229](https://github.com/peterramsing/lost/issues/229), [Less issue 974](https://github.com/less/less.js/issues/974)
+- If you're using [Less](http://lesscss.org/) you need to escape any `@lost` declarations like so: [See Issue 197](https://github.com/peterramsing/lost/issues/197#issuecomment-170324607)
+
+    ```less
+    .escape-at-rules(@literal) {
+        @namespace ~"lostgrid; @{literal}";
+    }
+
+    .escape-at-rules("@lost flexbox flex");
+    ```
 
 
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