Fast doc build (#4477)

* Create bash script for faster build

* Use git-dir in bashscript to change branch

* Better git command for checking out the pymc3-examples branch

* First change the pymc3 examples branch

* Address comments and suggestions on bash script

* Rename bash file according to comments

* Update fast_build_docs.sh

Change `sh` -> `bash` in shell script

Co-authored-by: Marco Gorelli <[email protected]>

Co-authored-by: Marco Gorelli <[email protected]>

Author: Pyrsos

fast_build_docs.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+git --git-dir=docs/source/pymc-examples/.git --work-tree=docs/source/pymc-examples checkout fast-docs-build
+pushd docs/source
+make clean
+make html
+popd