docs: update install how-to to @main

`@latest` for go install does not always pick up
the latest branch changes - `@main` seems to be 
more robust.

Author: toumorokoshi

README.md

@@ -33,7 +33,7 @@ It is useful for the following reasons:
 
 To install the binary, download it from the [releases page](https://github.com/aep-dev/aepcli/releases).
 
-Alternatively, you can install it using `go install github.com/aep-dev/aepcli/cmd/aepcli@latest`.
+Alternatively, you can install it using `go install github.com/aep-dev/aepcli/cmd/aepcli@main`.
 
 ## Usage Guide
 

docs/userguide.md

@@ -4,7 +4,7 @@
 
 To install the binary, download it from the [releases page](https://github.com/aep-dev/aepcli/releases).
 
-Alternatively, you can install it using `go install github.com/aep-dev/aepcli/cmd/aepcli@latest`.
+Alternatively, you can install it using `go install github.com/aep-dev/aepcli/cmd/aepcli@main`.
 
 ## Getting started