revise README

Author: jcupitt

Makefile.am

@@ -10,6 +10,7 @@ EXTRA_DIST = \
 	doc \
 	proj \
 	m4 \
+	screenshot.png \
 	nip2.desktop.in \
 	nip2.xml \
 	nip2.appdata.xml

README.md

@@ -8,23 +8,29 @@ library](https://libvips.github.io/libvips). It's a little like a spreadsheet:
 you create a set of formula connecting your objects together, and on a change
 nip2 recalculates.
 
+[![Screenshot](screenshot.png)](screenshot.png)
+
+## Installing
+
 You can probably install nip2 via your package manager. For
 Windows and OS X, you can download a binary from the [nip2 releases
-area](https://github.com/libvips/nip2/releases). Only read on if you want to
-compile yourself from source.
+area](https://github.com/libvips/nip2/releases). If you must build from
+source, see the section below.
 
-# Documentation
+## Documentation
 
 nip2 comes with a 50-page manual --- press F1 or Help / Contents in the
 program to view it.
 
-# Building nip2 from source
+## Building nip2 from source
 
-In the nip2 directory you should just be able to do:
+In the nip2 directory you should just be able to do the usual:
 
-	$ ./configure
-	$ make
-	$ sudo make install
+```
+./configure
+make
+sudo make install
+```
 
 By default this will install files to `/usr/local`.
 
@@ -33,60 +39,22 @@ nip2 needs in order to be able to build.
 
 If you downloaded from GIT you'll need:
 
-	$ ./autogen.sh
+```
+./autogen.sh
+```
 
 first to build the configure system. 
 
-# Dependencies
-
 nip2 needs vips, gtk2 and libxml2 at runtime and flex/bison at compile time.
 
-If you have fftw3, gsl, goffice, libgvc you get extra optional, but useful,
-features. 
-
-# Tips 
-
-production build with
-
-	./configure --prefix=/home/john/vips 
-
-debug build with
-
-	CFLAGS="-g -Wall" ./configure --prefix=/home/john/vips 
-
-(--enable-debug turns on and off automatically with development / production
-minor version numbers)
-
-leak check
-
-	export G_DEBUG=gc-friendly 
-	export G_SLICE=always-malloc 
-	valgrind --suppressions=/home/john/nip2.supp \
-	  --leak-check=yes \
-	  nip2 ... > nip2-vg.log 2>&1
-
-memory access check
-
-	valgrind --suppressions=/home/john/nip2.supp \
-	  --leak-check=no --db-attach=yes \
-	  nip2 ... > nip2-vg.log 2>&1
-
-or put "--suppressions=/home/john/nip2.supp" into ~/.valgrindrc 
-
-profiling
-
-	valgrind --tool=callgrind \
-	  --suppressions=/home/john/nip2.supp \
-	  nip2 ... > nip2-vg.log 2>&1
-
-Disclaimer: No guarantees of performance accompany this software, nor is any
-responsibility assumed on the part of the authors. Please read the licence
-agreement.
+If you have fftw3, gsl, goffice, libgvc you get extra features. 
 
-# snapcraft
+### snapcraft
 
 Rebuild snap with:
 
-	snapcraft cleanbuild 
+```
+snapcraft cleanbuild 
+```
 
 Though it's done automatically on a push.