PARQUET-1221: Extend release README

Author: Korn, Uwe <Uwe.Korn@blue-yonder.com>

Closes #441 from xhochy/PARQUET-1221 and squashes the following commits:

daa4778 [Korn, Uwe] PARQUET-1221: Extend release README [skip ci]
diff --git a/dev/release/README.md b/dev/release/README.md
index d9860cd..142ab64 100644
--- a/dev/release/README.md
+++ b/dev/release/README.md
@@ -17,7 +17,7 @@
 ==============
 
 1. Do a fresh `git clone` of the repository using the ASF git as origin.
-2. Set the git author to your gpg signing key.
+2. Set the git author to your gpg signing key using `git config --local user.email "<mail>"`.
 3. Create an RC using `./dev/release/release-candidate -r <rcNum> -v <version>` starting with `rcNum=0`.
    You could first do a dry-run by adding `-p` at the end.
 4. Check that the uploaded RC is valid using `./dev/release/verify-release-candidate <version> <rcNum>`.