README: add why section

README.md

@@ -0,0 +1,49 @@
+gphotos-cdp
+========
+
+What?
+--------
+
+This program uses the Chrome DevTools Protocol to drive a Chrome session that
+downloads your photos stored in Google Photos.
+By default, it starts at the most ancient item in the library, and progresses
+towards the most recent.
+It can be run incrementally, as it keeps track of the last item that was
+downloaded.
+It only works with the main library for now, i.e. it does not support the photos
+moved to Archive, or albums.
+For each downloaded photo, an external program can be run on it (with the -run
+flag) right after it is downloaded to e.g. upload it somewhere else. See the
+upload/perkeep program, which uploads to a Perkeep server, for an example.
+
+
+Why?
+--------
+
+We want to incrementally download our own photos out of Google Photos.
+
+Google Photos used to have an API to do this (the Picasa Web Albums API) but
+they removed it, replacing it with a new API that doesn't let you download your
+original photos. They instead let you download your photos with mangled EXIF,
+stripping location (and maybe recompressing the image bytes?).
+
+We can get our original photos out with Google Takeout, but only manually, and
+very slowly. We don't want to have to remember to do it (or remember to renew
+the time-limited scheduled takeouts) and we'd like our photos mirrored in
+seconds or minutes, not weeks.
+
+In https://github.com/perkeep/perkeep/issues/1144#issuecomment-525007239, Brad
+Fitzpatrick said that we might have to give up on APIs and resort to scraping,
+noting that the Chrome DevTools Protocol makes this pretty easy. Brad hacked up
+some Go code to drive Chrome (using https://github.com/chromedp/chromedp) and do
+a basic download and then Mathieu Lonjaret made this tool, fleshing out the
+idea.
+
+What if Google Photos breaks this tool on purpose or accident?
+--------
+
+I guess we'll have to continually update it.
+
+But that's no different than using people's APIs, because companies all seem to
+be deprecating and changing their APIs regularly too.
+

README.txt

@@ -1,16 +0,0 @@
-gphotos-cdp
-========
-
-This program uses the Chrome DevTools Protocol to drive a Chrome session that
-downloads your photos stored in Google Photos.
-By default, it starts at the most ancient item in the library, and progresses
-towards the most recent.
-It can be run incrementally, as it keeps track of the last item that was
-downloaded.
-It only works with the main library for now, i.e. it does not support the photos
-moved to Archive, or albums.
-For each downloaded photo, an external program can be run on it (with the -run
-flag) right after it is downloaded to e.g. upload it somewhere else. See the
-upload/perkeep program, which uploads to a Perkeep server, for an example.
-
-