BUILD.md:Windows:add temporary build instructions [skip ci]

Thank you for documenting this @mathusummut

(see also #37)

BUILD.md

@@ -64,7 +64,65 @@ libwxgtk3.0-dev libxml2-dev
 
 ### Windows
 
-(Need editing/updating)
+#### Temporary build instructions for Windows (subject to change):
+
+1. Make sure Visual Studio 2015 is installed.
+
+2. Make sure Git for Windows is installed.
+
+3. Make sure regular MegaGlest is installed.
+
+4. Open the command line from the directory you want to store the
+source code, and enter:
+
+    git clone https://github.com/ZetaGlest/zetaglest-source.git
+
+(if you think you may be contributing in the future, it's recommended
+to subsitute the URL listed above with the address of your fork)
+
+5. Now navigate to the source code directory, and in /mk/windows there
+is "build-mg-2015.bat". Run it.
+
+6. Copy the MegaGlest folder from Program Files or Program Files (x86)
+to somewhere else, and rename the copied folder to ZetaGlest.
+
+7. When the script is finished, there is megaglestx64.exe in
+/mk/windows. Rename it to zetaglest.exe.
+
+8. Copy zetaglest.exe, glest.ini and glestkeys.ini (which is in
+/mk/shared) into the ZetaGlest folder.
+
+9. From the same ZetaGlest folder, delete all directories except for
+the "blender" directory. Basically all that should be left is:
+   the blender folder, and the following files:
+
+    * 7z.dll
+    * 7z.exe
+    * glest.ini
+    * glestkeys.ini
+    * megaglest.ico
+    * megaglest_editorx64.exe
+    * megaglest_g3dviewerx64.exe
+    * megaglestx64.exe
+    * NetworkThrottleFix.reg
+    * OpenAL64.dll
+    * servers.ini
+    * uninstall.exe
+
+10. Create yet another temporary directory anywhere, open the command
+line from there and enter: "git clone
+https://github.com/ZetaGlest/zetaglest-data.git"
+
+11. After all the data is cloned into the temporary directory, copy all
+of its contents (the folders are: data, docs, maps...etc, and the files
+are MODS.md, README.md...etc) into the working ZetaGlest folder, right
+beside the executable.
+
+12. Run zetaglest.exe and enjoy!
+
+We are in the process of improving and updating the Windows build
+process. Please subscribe to the ticket below for updates:
+
 [Current Status](https://github.com/ZetaGlest/zetaglest-source/issues/37)
 
 ### *BSD