Merge bitcoin#17637: script: Add Keyserver to verify-commits README

bd6a243 script: Add Keyserver to verify-commits README (Emil Engler)

Pull request description:

  When I use the option with the default keyserver on `gpg (GnuPG) 2.2.12` from the Debian repositories only the keys from meshcollider and fanquake are actually found. Using the ubuntu keyserver works without any problems and all keys are getting found.
  As this keyserver is also suggested on [https://bitcoincore.org/en/download/](), it would be good to have a common keyserver.

ACKs for top commit:
  laanwj:
    ACK bd6a243, better to be explicit here

Tree-SHA512: d4127c42490390bed4e0074ebb1f8a6cc983f96bbea0ec1da011a93bed325a7f465ed9936e4bc2ef7c4b2e4501a2868d00b67ceb7bf85f2a902db9c6173a6c61

Author: MarcoFalke

contrib/verify-commits/README.md

@@ -40,7 +40,7 @@ Import trusted keys
 In order to check the commit signatures, you must add the trusted PGP keys to your machine. [GnuPG](https://gnupg.org/) may be used to import the trusted keys by running the following command:
 
 ```sh
-gpg --recv-keys $(<contrib/verify-commits/trusted-keys)
+gpg --keyserver hkp://keyserver.ubuntu.com --recv-keys $(<contrib/verify-commits/trusted-keys)
 ```
 
 Key expiry/revocation