BraveNewPipe: reflect the APK variants and add a quick building guide into README.md

.github/README.md

@@ -8,6 +8,14 @@ platforms work in the spirit of free speech, they could be integrated.
 Nevertheless, platforms that promote pornography or other degrading things will
 __NOT__ be included here.
 
+## APK variants
+Currently there are 3 variants:
+- `BraveNewPipe_v${TAG}.apk`: version most people want to install.
+- `BraveNewPipe_conscrypt_v${TAG}.apk`: like the first but with lastest TLS library aka conscrypt
+- `BraveNewPipe_legacy_v${TAG}.apk`: based on same code like above variants but with some checks to
+  make it work on SDK 19 aka Kitkat. [BraveNewPipeLegacy](https://github.com/bravenewpipe/BraveNewPipeLegacy)
+  is dumped instead. I hope this approach is more reliable and less a burden to maintain.
+
 ## Contribute
 This fork will focus only on integrating other platforms. Unrelated patches will
 be rejected for now.
@@ -29,3 +37,21 @@ Feel free to suggest which alternative platforms should be included. Any contrib
 Most problems with BraveNewPipe should be reported to the NewPipeExtractor
 project, as platform support is developed there.
 [Issues](../../../../NewPipeExtractor/issues)
+
+## Building the project
+Before building any flavor you should (if you want everything to be named BraveNewPipe) call the
+gradle task:
+```
+gradle bravify
+```
+For the `brave` and `braveConscrypt` flavor there is nothing special you have to do. But for the
+flavor `braveLegacy` you should also call before building:
+```
+gradle prepareLegacyFlavor
+```
+It will move some duplicated files from 'main' to a temp directory and alters the new version URL.
+Later if you want to restore the files after the Legacy flavor build (in case you want to build
+another flavor) run:
+```
+gradle unPrepareLegacyFlavor
+```