Add build instructions

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>

Author: deece

README.md

@@ -3,10 +3,16 @@ Tools to load/edit/create/panelize/prerender sets of gerber files.
 
 A recent build is available on http://blog.thisisnotrocketscience.nl/projects/pcb-panelizer/
 
-The .sln file (for VS2015 community edition) can be found in the GerberProjects folder.
-
 All tools are clean C# and will run fine under Mono.
 
 Please see http://www.thisisnotrocketscience.nl for news/updates/blogs
 
 Follow us on twitter: @rocket_not
+
+## Building
+### Visual Studio 2015 upwards
+Open the `GerberProjects/GerberProjects.sln` solution, convert it to your version of Visual Studio
+(if necessary), then build it. Dependencies should be fetched automatically via Nuget.
+
+### Linux
+Run `./build.sh`. Dependencies should be automatically fetched.