Adding readme.md for agnoster theme (#57)

themes/agnoster/README.md

@@ -0,0 +1,32 @@
+# agnoster
+
+In order for this theme to render correctly, you will need a
+[Powerline-patched font](https://gist.github.com/1595572).
+I recommend: https://github.com/powerline/fonts.git
+```
+git clone https://github.com/powerline/fonts.git fonts
+cd fonts
+install.sh
+```
+
+The aim of this theme is to only show you *relevant* information. Like most
+prompts, it will only show git information when in a git working directory.
+However, it goes a step further: everything from the current user and
+hostname to whether the last call exited with an error to whether background
+jobs are running in this shell will all be displayed automatically when
+appropriate.
+
+Generally speaking, this script has limited support for right
+prompts (ala powerlevel9k on zsh), but it's pretty problematic in Bash.
+The general pattern is to write out the right prompt, hit \r, then
+write the left. This is problematic for the following reasons:
+- Doesn't properly resize dynamically when you resize the terminal
+- Changes to the prompt (like clearing and re-typing, super common) deletes the prompt
+- Getting the right alignment via columns / tput cols is pretty problematic (and is a bug in this version)
+- Bash prompt escapes (like \h or \w) don't get interpolated
+
+all in all, if you really, really want right-side prompts without a
+ton of work, recommend going to zsh for now. If you know how to fix this,
+would appreciate it!
+
+![ScreenShot](agnoster-bash-sshot.png)