contrib: Replace developer keys with list of pgp fingerprints

Author: MarcoFalke

contrib/gitian-keys/README.md

@@ -1,16 +1,26 @@
-PGP keys
-========
+## PGP keys of Gitian builders and Developers
 
-This folder contains the public keys of developers and active contributors.
+This list contains the public keys of Gitian builders and active developers.
 
 The keys are mainly used to sign git commits or the build results of Gitian
 builds.
 
-You can import the keys into gpg as follows. Also, make sure to fetch the
-latest version from the key server to see if any key was revoked in the
-meantime.
+The most recent version of each pgp key can be found on most pgp key servers.
+
+Fetch the latest version from the key server to see if any key was revoked in
+the meantime.
+To fetch the latest version of all pgp keys in your gpg homedir,
 
 ```sh
-gpg --import ./*.pgp
 gpg --refresh-keys
 ```
+
+To fetch keys of Gitian builders and active developers, feed the list of
+fingerprints of the primary keys into gpg:
+
+```sh
+while read fingerprint keyholder_name; do gpg --keyserver hkp://subset.pool.sks-keyservers.net --recv-keys ${fingerprint}; done < ./keys.txt
+```
+
+Add your key to the list if you provided Gitian signatures for two major or
+minor releases of Bitcoin Core.