New `alias gfa=git fetch --all` for git module

Also includes an updated README.md !

modules/git/README.md

@@ -93,6 +93,7 @@ Aliases are enabled by default. You can disable them with:
 ### Fetch
 
   - `gf` downloads objects and references from another repository.
+  - `gfa` downloads objects and references from all remote repositories.
   - `gfc` clones a repository into a new directory.
   - `gfm` fetches from and merges with another repository or local branch.
   - `gfr` fetches from and rebases on another repository or local branch.

modules/git/alias.zsh

@@ -77,6 +77,7 @@ if ! zstyle -t ':prezto:module:git:alias' skip 'yes'; then
 
   # Fetch (f)
   alias gf='git fetch'
+  alias gfa='git fetch --all'
   alias gfc='git clone'
   alias gfm='git pull'
   alias gfr='git pull --rebase'