readme(tracker): build-readme for js packages

tracker/README.md

@@ -0,0 +1,31 @@
+## Local build
+
+
+In order to build locally any of the javascript packages located under this directory, go to the corresponding folder first:
+
+```sh
+cd tracker	# or any tracker-* plugin
+
+```
+Then run 
+```sh
+yarn		
+yarn build  
+```
+OR
+
+```sh
+npm i	
+npm run build  
+```
+
+You can then use it as a local javascript package by executing the folowing line under your local project location:
+
+```sh
+yarn add file:../path/to/openreplay/monorepo/tracker/tracker
+````
+OR
+```sh
+npm install --save ../path/to/openreplay/monorepo/tracker/tracker
+```
+