Change pCodecParameters to pLocalCodecParameters in README.md

Hi, I noticed this line of code in README.md

printf("\tCodec %s ID %d bit_rate %lld", pLocalCodec->long_name, pLocalCodec->id, pCodecParameters->bit_rate);

in which pLocalCodec is not declared in the article before used which might cause confusion in my view. Digging into the c code, I found this line.

https://github.com/leandromoreira/ffmpeg-libav-tutorial/blob/cdd616ce871078ebb67601af207f10a299914e19/0_hello_world.c#L110

As for a guess, maybe the author firstly write the c code and copy-and-paste these important parts into README and lead to this issue. By the way, I think adding \n afterward printfs could make output looks better. Hope that useful.

UPDATE
This line of code has the same problem:

AVCodecContext *pCodecContext = avcodec_alloc_context3(pCodec);

Maybe it will be better to replace pCodec with pLocalCodec.

Open README.md and compare the affected snippets with 0_hello_world.c at the linked line 110. Update the undeclared codec variable references in the README, and review the requested newline additions to the printf examples. Done means the README snippets use the declared variables and present the intended output clearly.