Add $(nproc) to make documentation (#9360)

src/README.md

diff --git a/src/README.md b/src/README.md
index 9db40fd..80e8668 100644
--- a/src/README.md
+++ b/src/README.md
@@ -48,7 +48,7 @@
 
 
      ./configure
-     make
+     make -j$(nproc) # $(nproc) ensures it uses all cores for compilation
      make check
      sudo make install
      sudo ldconfig # refresh shared library cache.