Add npm scripts in build guide

Author: Anesh Parvatha

.env.staging

@@ -3,20 +3,4 @@
 SKIP_PREFLIGHT_CHECK=true
 
 //the variable declaration should start with REACT_APP_
-//Eg:-REACT_APP_ENV=development
-
-REACT_APP_NKB_BASE_URL = https://nkb-backend-10xiitian-staging-apis.ibhubs.in/api/
-
-REACT_APP_GTM_ID = GTM-TT9MHTQ
-
-REACT_APP_GOOGLE_SITE_VERIFICATION = ''
-
-REACT_APP_USERSNAP_ID = ''
-
-REACT_APP_SEGMENT_ID = 9HHiENJNjKhD6JdpJVegnRLkWqwyvToR
-
-REACT_APP_SENTRY_KEY=https://[email protected]/1852258
-
-REACT_APP_ONE_SIGNAL_APP_ID = 997515ae-d139-4fcd-992f-e520a8522cdc
-
-REACT_APP_PROGRAM_SLUGS_URL = https://nkb-backend-media-static-tenxiitian.s3.ap-south-1.amazonaws.com/tenxiitian_prod/website-static/jsons/staging/slugs.json
+//Eg:-REACT_APP_ENV=development

docs/how-to-build.md

@@ -59,3 +59,15 @@ This is the build which we push to `production` environment. Run below command t
 ```
 yarn build:master
 ```
+
+If you want to customize any of the above build commands, you need to modify npm scripts written in `package.json`.
+
+```
+{
+    "build": "GENERATE_SOURCEMAP=false react-scripts build",
+    "build:beta": "set \"CI=false\" && env-cmd -f .env.beta yarn build",
+    "build:gamma": "set \"CI=false\" && env-cmd -f .env.gamma yarn build",
+    "build:staging": "set \"CI=false\" && env-cmd -f .env.staging yarn build",
+    "build:master": "set \"CI=false\" && env-cmd -f .env.production yarn build",
+}
+```