Merge pull request #792 from veox/doc-crypto-secp256k1

doc: crypto/secp256k1 GMP dependency package name.

crypto/secp256k1/README.md

@@ -7,8 +7,11 @@ Implements cryptographic operations for the secp256k1 ECDSA curve used by Bitcoi
 
 Installing
 ===
+
+GMP library headers are required to build. On Debian-based systems, the package is called `libgmp-dev`.
+
 ```
-sudo apt-get install gmp-dev
+sudo apt-get install libgmp-dev
 ```
 
 Now compiles with cgo!