doc: fix README.md file diagram

[cruelyf]

Purpose of the PR

• To update the Readme.md file. The Readme.md file has a small error representing the HugeGraph Ecosystem Integration diagram.

Main Changes

• The Readme.md file has a small error representing the HugeGraph Ecosystem Integration diagram. I fixed it with adding spaces.

Verifying these changes

• Trivial rework / code cleanup without any test coverage. (No Need)
• Already covered by existing tests, such as (please modify tests here).
• Need tests and can be verified as follows.

Does this PR potentially affect the following parts?

• Nope
• Dependencies (add/update license info)
• Modify configurations
• The public API
• Other affects (typed here)

Documentation Status

• Doc - TODO
• Doc - Done
• Doc - No Need