README: specify source tarballs for the Building heading

LDVG · LDVG · commit e3ad7e6cb7b9 · 2025-02-26T16:42:49.000+01:00
diff --git a/README b/README
@@ -50,8 +50,7 @@ $ brew install pam-u2f
 ----
 
 [[building]]
-== Building
-
+== Building from a source tarball
 
 This project uses 'autoconf', 'automake', 'pkg-config' and 'libtool'
 to achieve portability and ease of use.
