More detailed instructions for building are needed

The README says only
```
make all
```
However it doesn't state (neither does the project webpage) that it depends on Lua development files, that need to be installed on the system, more so that it depends on specific version 5.2. I had to find this out by reading the Makefile after encoutering build errors.

In the end i managed to build this in Ubuntu 18, but only after installing package `liblua5.2-dev` and manually creating symbolic link `ln -s -T liblua5.2.so /usr/lib/x86_64-linux-gnu/liblua.so` or changing the Makefile's link parameter from `-llua` to `-llua5.2`.

I also managed to build and run it in Windows under Msys2, by installing package `mingw-w64-x86_64-lua-5.3.5-1`. In Msys2 repositories, there is no lua 5.2, only 5.1 and 5.3, but the 5.3 seems to work with it.

This should all be written somewhere - in README.md, at the official page, it doesn't matter, but somewhere where the user discovers it when trying it out. Also, the promissed Windows binaries at http://websocketserver.de/#c-download are nowhere to be found, not on the page, not here on github.

By the way, that link parameter `-llua` is at wrong place, it has to be at the end of the line:
```$(CC) -g -o $@ $^ -llua```
instead of
```$(CC) -g -llua -o $@ $^```
otherwise it leads to undefined reference linker errors with gcc.