update and fix some installation docs

INSTALL.txt

@@ -1,9 +1,9 @@
 Installation is the same as any python package, e.g.:
 
-wget --no-check-certificate https://bitbucket.org/pyspeckit/pyspeckit.bitbucket.org/get/tip.tar.gz
-tar -xzf pyspeckit-pyspeckit.bitbucket.org-tip.tar.gz 
-cd pyspeckit-pyspeckit.bitbucket.org-tip
+wget --no-check-certificate https://github.com/pyspeckit/pyspeckit/archive/master.zip
+unzip master.zip
+cd pyspeckit
 python setup.py install
 
 or if you have pip:
-pip install https://bitbucket.org/pyspeckit/pyspeckit.bitbucket.org/get/tip.tar.gz
+pip install https://github.com/pyspeckit/pyspeckit/archive/master.zip

docs/install_via_GitHub.rst

@@ -1,6 +1,28 @@
 Install pyspeckit via GitHub
 ============================
 
+Quick
+-----
+
+You can pip install the development version of pyspeckit::
+
+    pip install https://github.com/pyspeckit/pyspeckit/archive/master.zip
+
+
+Installing a branch
+-------------------
+
+If there's a bugfix branch, e.g., from a pull request, you can install it in a similar way.  Just replace the branch name::
+
+    pip install https://github.com/pyspeckit/pyspeckit/archive/{branchname}.zip
+
+
+
+More detailed
+-------------
+
+If you want to help develop pyspeckit, follow these instructions:
+
 Logged into your github account, go to https://github.com/pyspeckit/pyspeckit
 and click “Fork” in upper right.