Update documentation.

Author: chromice

README.md

@@ -411,8 +411,9 @@ These mixins let you set the respective CSS property in grid columns.
 ##### Parameters
 
 1. *number* `@span` – number of columns
-2. (optional) *pixel* `@nudge` – amount of units to nudge
-3. (optional) *number* `@base` – parent width in columns (`@grid-columns` by default)
+2. (optional) *pixel* `@nudge` – amount of pixels to nudge
+3. (optional) *number* `@base` – parent width in columns
+4. (optional) *pixel* `@base-nudge` – amount of pixels parent width was nudged by
 
 ##### Usage
 
@@ -424,15 +425,17 @@ div {
 }
 ```
 
+
 #### `.left()`, `.right()`, `.margin-left()`, `.margin-right()`, `.padding-left()`, `.padding-right()`
 
 These mixins let you set the respective CSS property in grid columns.
 
 ##### Parameters
 
 1. (optional) *number* `@span` – number of columns the property spans
-2. (optional) *pixel* `@nudge` – amount of units to nudge
-3. (optional) *number* `@base` – parent width in columns (`@grid-columns` by default)
+2. (optional) *pixel* `@nudge` – amount of pixels to nudge
+3. (optional) *number* `@base` – parent width in column
+4. (optional) *pixel* `@base-nudge` – amount of pixels parent width was nudged by
 
 **NB!** You must specify either `@span` or `@nudge`!