gitignore: slight changes so that it might be reused as dockerignore

This diff should not change what is matched by gitignore
(e.g. `build/` matches `contrib/build-wine/build/`).
I am experimenting with reusing gitignore as dockerignore which uses
slightly different semantics.

related: https://github.com/spesmilo/electrum/pull/7431#discussion_r677541811

.gitignore

@@ -1,5 +1,6 @@
+.git/
 ####-*.patch
-*.pyc
+**/*.pyc
 *.swp
 build/
 dist/
@@ -27,6 +28,9 @@ electrum_data
 
 # build workspaces
 contrib/build-wine/tmp/
+contrib/build-wine/build/
+contrib/build-wine/.cache/
+contrib/build-wine/dist/
 contrib/build-wine/signed/
 contrib/build-wine/fresh_clone/
 contrib/build-linux/sdist/fresh_clone/
@@ -34,12 +38,12 @@ contrib/build-linux/appimage/build/
 contrib/build-linux/appimage/.cache/
 contrib/build-linux/appimage/fresh_clone/
 contrib/osx/.cache/
+contrib/osx/build-venv/
 contrib/android/fresh_clone
 contrib/android/android_debug.keystore
 contrib/secp256k1/
 contrib/zbar/
 contrib/libusb/
-contrib/osx/build-venv/
 
 # shared objects
 electrum/*.so