Typo on README.md instructions

[Robertorosmaninho]

Hey, team, just a small correction here! There is a small typo in

2. Build with CMake:

   cd build
   cmake ..
   make -j $(nrpoc)
   

It's written nrpoc instead of nproc.

[Robertorosmaninho]

There is also a mismatch between the README instructions and the tool installed.
The README says the name of the tool is proof-producer. However, this binary isn't installed

$ sudo apt install proof-producer
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
proof-producer is already the newest version (1.3.1).
The following packages were automatically installed and are no longer required:
  catch2 libspdlog1 lld-14
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 76 not upgraded.

$ proof-generator --help
zsh: command not found: proof-generator

The binaries installed are named:

proof-generator-single-threaded
proof-generator-multi-threaded