chore: Fix URLs in md (#297)

Fixes #296 

This change is to fix URLs that return 404 errors.

---
By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license

Author: tacck

packages/@aws-cdk/cloud-assembly-schema/README.md

@@ -5,8 +5,8 @@ This module is part of the [AWS Cloud Development Kit](https://github.com/aws/aw
 ## Cloud Assembly
 
 The _Cloud Assembly_ is the output of the synthesis operation. It is produced as part of the
-[`cdk synth`](https://github.com/aws/aws-cdk/tree/main/packages/aws-cdk#cdk-synthesize)
-command, or the [`app.synth()`](https://github.com/aws/aws-cdk/blob/main/packages/@aws-cdk/core/lib/app.ts#L135) method invocation.
+[`cdk synth`](https://github.com/aws/aws-cdk-cli/tree/main/packages/aws-cdk#cdk-synthesize)
+command, or the [`app.synth()`](https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/core/lib/stage.ts#L219) method invocation.
 
 Its essentially a set of files and directories, one of which is the `manifest.json` file. It defines the set of instructions that are
 needed in order to deploy the assembly directory.
@@ -51,4 +51,3 @@ cannot be guaranteed because some instructions will be ignored.
 ## Contributing
 
 See [Contribution Guide](./CONTRIBUTING.md)
-

packages/@aws-cdk/node-bundle/README.md

@@ -151,4 +151,4 @@ Note that this will balloon up the package size significantly.
 If you are bundling a CLI application that also has top level exports, we suggest to extract
 the CLI functionality into a function, and add this function as an export to `index.js`.
 
-> See [aws-cdk](https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk/bin/cdk.ts) as an example.
+> See [aws-cdk](https://github.com/aws/aws-cdk-cli/blob/main/packages/aws-cdk/bin/cdk) as an example.

packages/aws-cdk/README.md

@@ -536,7 +536,7 @@ and might have breaking changes in the future.
 - `Fn::Split`
 - `Fn::Sub`
 
-> *: `Fn::GetAtt` is only partially supported. Refer to [this implementation](https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk/lib/api/evaluate-cloudformation-template.ts#L477-L492) for supported resources and attributes.
+> *: `Fn::GetAtt` is only partially supported. Refer to [this implementation](https://github.com/aws/aws-cdk-cli/blob/main/packages/aws-cdk/lib/api/cloudformation/evaluate-cloudformation-template.ts#L256-L266) for supported resources and attributes.
 
 ### `cdk rollback`