Adding the example of usage of -p,--parameter <param-name param-value> (#55)

* Adding the example of usage of -p,--parameter <param-name param-value>

This is a port of the PR #54 as the commit

* Update README.md

Incorporated changes as suggested by @afelisatti

Co-authored-by: Julian Miras Hernandez <julian.miras@mulesoft.com>

Author: machaval

README.md

@@ -287,6 +287,19 @@ curl https://jsonplaceholder.typicode.com/posts/1 | dw "output application/json
 }
 ```
 
+### Using parameters
+Using the internal map `params`, we can access injected parameters in the command line with the `-p` option
+```
+dw -p myName Julian "output json --- { name : params.myName }"
+```
+#### Output
+```
+{
+  "name": "Julian"
+}
+```
+
+
 ## Contributions Welcome
 
 Contributions to this project can be made through Pull Requests and Issues on the