Add readme

Author: Jose Alberto Calvo Vargas

drop_column/README.MD

@@ -0,0 +1,33 @@
+# Alter datasource removing a column
+
+[Pull Request](https://github.com/tinybirdco/use-case-examples/pull/347)
+
+- Just remove the column from the schema and apply the changes. If there are dependent materialized views the CLI will list them and ask for confirmation.
+
+
+```diff
+SCHEMA >
+-    `version` LowCardinality(String) `json:$.version`,
+```
+
+- Create a PR with the change above, a new branch will be created as part of the CI process. You can double check the changes checking the datasource schema.
+
+- To deploy the change, merge to PR to you main branch, the CD job will run and will deploy the changes.
+
+```
+...
+** Diffs from current commit 'fa782bcbd6907ba013b46c91097949e9413beaa1' and new '6dc57d17508da520fec72c1e970c736400c4cd38':
+	modified:	alter_default_value_in_column/datasources/analytics_events.datasource
+** Preparing commit ...
+** Processing ./datasources/analytics_events.datasource
+** Building dependencies
+** [DRY RUN] Deploying commit ...
+** [DRY RUN] Running 'analytics_events' 
+** Deploying commit ...
+** Running 'analytics_events' 
+** The description or schema of 'analytics_events' has changed.
+**   -  DROP COLUMN `version
+** The Data Source has been correctly updated.
+** 'analytics_events' created
+...
+```