adding arm64 build, and improved termux installation process

* Added arm64 Linux standalone build. (No autobuilder yet.)
* Improved termux installation process.

Added git-annex-install.sh script to avoid user needing to type as much in
termux. The scope of this script is limited; runshell handles the rest.

Runshell runs termux-fix-shebang on the shell scripts. The problem is
the bundled bin/sh script, deleting that script also works, but then the
others probably use the system Android /bin/sh, which could be old or
broken or not posix or whatever. Using termux sh to run the scripts is
better.

This commit was sponsored by Eric Drechsel on Patreon.

doc/tips/install_on_Android_in_Termux.mdwn

@@ -4,13 +4,9 @@ Linux software in a terminal.
 git-annex is not currently part of the Termux distribution, but it's easy
 to install it. Paste these commands into Termux:
 
-	pkg install git wget tar coreutils proot
-	termux-setup-storage
-	cd
-	wget https://downloads.kitenet.net/git-annex/linux/current/git-annex-standalone-armel.tar.gz
-	tar zxf git-annex-standalone-armel.tar.gz
-	rm git-annex-standalone-armel.tar.gz
-	git-annex.linux/runshell
+	pkg install wget
+	wget https://git-annex.branchable.com/install/Android/git-annex-install.sh
+	sh git-annex-install.sh
 
 Now you can set up a git-annex repository or two, to manage your
 Android files. To avoid typing any more, you can start up the
@@ -34,7 +30,7 @@ well in this Termux environment.
 ## Starting on boot
 
 If you install the Termux:Boot app, git-annex will also integrate with it.
-Repositories you create with the webapp (or list in
+Repositories you create with the webapp (or listed in
 ~/.config/git-annex/autostart) will have the assistant started in them on
 boot, so you don't need to start it manually.
 
@@ -46,3 +42,8 @@ boot, so you don't need to start it manually.
   limitations of Android's /sdcard. You can get around this using v6
   unlocked repositories, or by putting the git-annex repository on a better
   filesystem on the Android device, such as your termux home directory.
+
+## Upgrading
+
+To upgrade to a new git-annex release, just run
+`git-annex-install.sh` again.

doc/tips/install_on_Android_in_Termux/comment_1_dc277facdcfba4e175831467b0e450d5._comment

@@ -0,0 +1,8 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 1"""
+ date="2018-10-11T17:26:38Z"
+ content="""
+Bunch of old comments about problems with this that have been fixed were
+moved to [[old_comments]].
+"""]]

doc/tips/install_on_Android_in_Termux/old_comments.mdwn

@@ -0,0 +1 @@
+Some old comments, all obsoleted now. --[[Joey]]