Update tdlib_ping workflow and README to enhance CGO_CFLAGS configuration for building TDLib. Clarify the inclusion of the build directory in the CFLAGS to improve user experience when compiling from source.

cmd/tdlib_ping/README.md

@@ -36,7 +36,8 @@ go build -tags=tdlib -o tdlib_ping ./cmd/tdlib_ping
 
 ```bash
 export CGO_ENABLED=1
-export CGO_CFLAGS="-I/path/to/td-clone"
+# Корень клона + каталог cmake build (там tdjson_export.h после target tdjson).
+export CGO_CFLAGS="-I/path/to/td-clone -I/path/to/td-clone/build"
 export CGO_LDFLAGS="-L/path/to/td-clone/build -ltdjson"
 go build -tags=tdlib -o tdlib_ping ./cmd/tdlib_ping
 ```