State explicitly that pkg-config is required

README.rst

@@ -155,6 +155,7 @@ distribution you use):
 * libxml2-dev      (Required for Metalink support)
 * zlib1g-dev       (Required for gzip, deflate decoding support in HTTP)
 * libsqlite3-dev   (Required for Firefox3/Chromium cookie support)
+* pkg-config       (Required to detect installed libraries)
 
 You can use libgcrypt-dev instead of nettle-dev and libgmp-dev:
 
@@ -170,8 +171,6 @@ You can use libexpat1-dev instead of libxml2-dev:
 
 * libexpat1-dev    (Required for Metalink support)
 
-You may also need pkg-config to detect the above mentioned libraries.
-
 On Fedora you need the following packages: gcc, gcc-c++, kernel-devel,
 libgcrypt-devel, libgcrypt-devel, libxml2-devel, openssl-devel