Add to readme

Author: marekweb

README.md

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-# find-replace (Sourcegraph extension)
+# Find-replace campaigns (Sourcegraph extension)
 
-Perform a find-replace over multiple repositories by creating a Sourcegraph campaign.
+Create Sourcegraph campaigns that perform a find-replace on multiple files in multiple repositories.
+
+## What are Sourcegraph campaigns?
+
+Campaigns let you make code changes across many repositories and code hosts. Read more about [campaigns in the Sourcegraph docs.](https://docs.sourcegraph.com/campaigns)
+
+## How does a find-replace campaign work?
+
+A find-replace campaign is a campaign that finds all matches of a given string and replaces them with a replacement string.
+
+- Perform a search on Sourcegraph
+- In the search results toolbar, click "Find-replace"
+- Enter the string to find
+- Enter the replacement string
+- Once the process is complete, click the notification to open the newly created campaign.