Add errors.md (#2)

* Add errors.md

* refer to errors.md

* Update errors.md

* Update errors.md

* Update errors.md

Author: mannprerak2

pkgs/ffigen/errors.md

@@ -0,0 +1,23 @@
+# Errors in ffigen
+
+This file documents various errors and their potential fixes related to ffigen.
+
+## Errors in source header files
+
+Under the hood ffigen uses libclang to parse header files. Any compiler warnings/errors should be logged (with SEVERE level), these should be resolved as it can potentially generate *incomplete* or *invalid* bindings that might cause silent errors at runtime.
+
+> You can pass in args to libclang using  `compiler-opts` via cmd line or yaml config or both.
+
+Here we'll list some common usecases. You can find the full list of [supported args here](https://clang.llvm.org/docs/ClangCommandLineReference.html#id5).
+
+### Missing headers
+
+These are the most common source file errors. You can specify [include paths to clang](https://clang.llvm.org/docs/ClangCommandLineReference.html#id6) like this 
+```yaml
+compiler-opts:
+  - "-I/path/to/folder"
+```
+
+### Ignoring source errors
+
+As a last resort, you can pass in `--ignore-source-errors` or set `ignore-source-errors: true` in yaml config.

pkgs/ffigen/lib/src/header_parser/parser.dart

@@ -123,7 +123,7 @@ List<Binding> parseToBindings(Config c) {
       _logger.warning("Ignored source errors. (ObjC)");
     } else {
       _logger.severe(
-          "Skipped generating bindings due to errors in source files. Either resolve or ignore them (Set --ignore-source-errors on cmd or ignore-source-errors:true in config.");
+          "Skipped generating bindings due to errors in source files. See https://github.com/dart-lang/native/blob/main/pkgs/ffigen/errors.md.");
       exit(1);
     }
   }