Describe unset command in readme

Author: gopinath-langote

1build.yaml

@@ -1,6 +1,3 @@
 project: gopi
-before: echo b
-after: echo 1
 commands:
-  - b: echo han
   - test: go test -v -cover github.com/gopinath-langote/1build/testing -run . GOCACHE=off

README.md

@@ -73,6 +73,12 @@ the things that actually matter.
    ```console
    1build set lint "eslint server.js"
    ```
+### Remove/Unset existing configuration
+
+- Unset command configuration for `lint`
+   ```console
+   1build unset lint
+   ```
 
 ### Using `before` and `after` commands
 Consider that your project requires some environment variables to set before running any