gnu: mpfr: Edit synopsis & description.

* gnu/packages/multiprecision.scm (mpfr)[synopsis, description]: Edit.
Define MPFR.

gnu/packages/multiprecision.scm

@@ -98,10 +98,11 @@ (define-public mpfr
    (build-system gnu-build-system)
    (outputs '("out" "debug"))
    (propagated-inputs `(("gmp" ,gmp)))            ; <mpfr.h> refers to <gmp.h>
-   (synopsis "C library for arbitrary precision floating-point arithmetic")
+   (synopsis "C library for arbitrary-precision floating-point arithmetic")
    (description
-    "GNU MPFR is a C library for performing multiple-precision,
-floating-point computations with correct rounding.")
+    "GNU@tie{}@dfn{MPFR} (Multiple Precision Floating-Point Reliably) is a C
+library for performing multiple-precision, floating-point computations with
+correct rounding.")
    (license lgpl3+)
    (home-page "http://www.mpfr.org/")))