docs: update project documentation and requirements

- Add requirements section to README file

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

Author: appleboy

README.md

@@ -2,6 +2,13 @@
 
 A command line tool build with Golang to migrate a [Bitbucket Server](https://www.atlassian.com/software/bitbucket/enterprise) (Data Center) Project to Gitea. See the [V1 REST API](https://developer.atlassian.com/server/bitbucket/rest/v815/intro/#about).
 
+## Requirements
+
+The following software is required to run this tool:
+
+* Gitea version: **1.21.3**
+* Bitbucket Server version: **8.9.7**
+
 ## Initial Setup
 
 Setup the Gitea and Bitbucket config