Add prunegone alias to README and create corresponding script

Author: Magnus167

README.md

@@ -17,6 +17,8 @@ GitHub Repo : https://github.com/Magnus167/git-aliases
 	cop = "!f() { git checkout $1 && git pull; }; f"
 	cob = checkout -b
 	branchr = branch --sort=-committerdate
+	prunegone = !git fetch --prune && git branch -vv | awk '/: gone]/{print $1}' | xargs -r git branch -d
+
 	pr = "!f() { BRANCH=$(git branch --show-current); REPOURL=$(git config --get remote.origin.url); python ~/git-aliases/python/getpr.py $REPOURL $BRANCH; }; f"
 	co-pr = "!f() { REPOURL=$(git config --get remote.origin.url); BRANCH=$(python ~/git-aliases/python/checkoutpr.py $REPOURL $1); git checkout $BRANCH; git pull; }; f"
 ```

aliases/prunegone.sh

@@ -0,0 +1,17 @@
+# # prunegone
+# ## Usage:
+# ```bash
+# git prunegone
+# ```
+# ## Intended use
+# Use this alias to delete all branches that are gone on the remote.
+# It does not delete branches that are not gone on the remote, or are
+# not on the remote at all.
+# 
+# Running this alias executes:
+# ```bash
+# git fetch --prune
+# git branch -vv | awk "/: gone]/{print \$1}" | xargs -r git branch -d
+# ```
+
+git config --global alias.prunegone '!git fetch --prune && git branch -vv | awk "/: gone]/{print \$1}" | xargs -r git branch -d'