Adding documentation.

Author: grasmash

phing/tasks/setup.xml

@@ -228,8 +228,6 @@
   </target>
 
   <target name="setup:git-hooks" description="Installs git hooks to local .git/hooks directory from version controlled scripts/git-hooks directory.">
-    <echo level="verbose">Removing ${repo.root}/.git/hooks, if it exists.</echo>
-
     <exec dir="${repo.root}/.git" command="mkdir -p hooks" logoutput="true" checkreturn="true" level="${blt.exec_level}" passthru="true"/>
     <delete file="${repo.root}/.git/hooks/pre-commit" failonerror="false" quiet="true" verbose="${blt.verbose}"/>
     <delete file="${repo.root}/.git/hooks/commit-msg" failonerror="false" quiet="true" verbose="${blt.verbose}"/>

readme/extending-blt.md

@@ -86,6 +86,24 @@ More specifically, you can modify the build artifact in the following key ways:
             dir: ${deploy.dir}/docroot/profiles/contrib/lightning
             command: npm run install-libraries
 
+### setup:*
+
+#### setup:git-hooks
+
+You may disable a git hook by setting its value under `git.hooks` to false:
+
+        git:
+          hooks:
+            pre-commit: false
+
+You may use a custom git hook in place of BLT's default git hooks by setting its value under `git.hooks` to the directory path containing of the hook. The directory must contain an executable file named after the git hook:
+
+        git:
+          hooks:
+            pre-commit: ${repo.root}/my-custom-git-hooks
+
+In this example, an executable file named `pre-commit` should exist in `${repo.root}/my-custom-git-hooks`.
+
 ### tests:*
 
 #### tests:behat