Add gitlab.com/tozd/go/errors. (#5049)

README.md

@@ -1027,6 +1027,7 @@ _Libraries for handling errors._
 - [errors](https://github.com/emperror/errors) - Drop-in replacement for the standard library errors package and github.com/pkg/errors. Provides various error handling primitives.
 - [errors](https://github.com/neuronlabs/errors) - Simple golang error handling with classification primitives.
 - [errors](https://github.com/PumpkinSeed/errors) - The most simple error wrapper with awesome performance and minimal memory overhead.
+- [errors](https://gitlab.com/tozd/go/errors) - Providing errors with a stack trace and optional structured details. Compatible with github.com/pkg/errors API but does not use it internally.
 - [errors](https://github.com/bnkamalesh/errors) - Drop-in replacement for builtin Go errors. This is a minimal error handling package with custom error types, user friendly messages, Unwrap & Is. With very easy to use and straightforward helper functions.
 - [errors](https://github.com/cockroachdb/errors) - Go error library with error portability over the network.
 - [errorx](https://github.com/joomcode/errorx) - A feature rich error package with stack traces, composition of errors and more.