chore: update README (#1449)

Author: Takashi Matsuo

README.md

@@ -1,15 +1,6 @@
-![Diagram of relationship between Autosynth, Synthtool, and Github](./images/flow.png)
-
 # SynthTool (for client libraries)
 
-This repository contains two, related tools for generating source code for
-Google Cloud client libraries.
-
-## Synthtool
-
 Synthtool is a library of common templates and code that makes generating
-source code easier.  With synthtool, the source code for an API can be generated
-in 10 lines of code or less.  For an example, see 
-[googleapis/java-asset/synth.py](https://github.com/googleapis/java-asset/blob/master/synth.py).
+source code easier.
 
-More details about Synthtool can be found in its [README](./synthtool/README.md).
+See the inner [README](./synthtool/README.md) for more details.