Simplify README

At present some of this is simply wrong, so drop it.
Probably the first part wants revising too.

README.md

@@ -1,5 +1,5 @@
 siunitx - A comprehensive (SI) units package
-==============================================
+============================================
 
 Physical quantities have both numbers and units, and each
 physical quantity should be expressed as the product of a number
@@ -15,41 +15,3 @@ of configuration options which make it possible to follow
 varying typographic conventions with the same input syntax. The
 package includes automated processing of numbers and units, and
 the ability to control tabular alignment of numbers.
-
-Installation
-------------
-
-The package is supplied in `dtx` format and as a pre-extracted
-zip file, `siunitx.tds.zip`. The later is most convenient for
-most users: simply unzip this in your local texmf directory . If
-you want to unpack the `.dtx` yourself, running `tex
-siunitx.dtx` will extract the package whereas `latex
-siunitx.dtx` will extract it and also typeset the documentation.
-
-The package requires LaTeX3 support as provided in the
-`l3kernel` and `l3packages` bundles. Both of these are available
-on [CTAN](http://www.ctan.org/) as ready-to-install zip files.
-Suitable versions are available in MiKTeX 2.9 and TeX Live 2012
-(updating the relevant packages online may be necessary).
-LaTeX3, and so `siunitx`, requires the e-TeX extensions: these
-are available on all modern TeX systems.
-
-Typesetting the documentation requires a number of packages in
-addition to those needed to use the package. This is mainly
-because of the number of demonstration items included in the
-text. To compile the documentation without error, you will
-need the packages:
- - `amsmath`
- - `booktabs`
- - `cancel`
- - `caption`
- - `cleveref`
- - `colortbl`
- - `csquotes`
- - `datatool`
- - `helvet`
- - `mathpazo`
- - `multirow`
- - `listings`
- - `pgfplots`
- - `xcolor`