Add repo build information to the Debian README.

pkg/debian/README

@@ -1,6 +1,12 @@
 This directory contains the build runner script for creating .DEB packages for
 Debian and Ubuntu. 
 
+Supported platforms
+===================
+
+Debian 9 & 10
+Ubuntu 16.04, 18.04, 19.04 & 19.10
+
 Build configuration
 ===================
 
@@ -35,13 +41,115 @@ pgadmin4-web_<version>_<distro>_<distro_version>_<arch>.deb
   The server mode setup script for configuring Apache HTTPD. Requires the 
   server package.
 
-Supported platforms
+Building a repo
-===================
+===============
 
-Debian 9 & 10
+An APT repo can be created by building DEBs for the required platforms, moving
-Ubuntu 16.04, 18.04, 19.04 & 19.10
+them into the required directory structure, and then running a number of
+commands to create the required metadata. The pgAdmin repos use the following
+structure (which doesn't entirely follow the normal structure for APT, but
+does seem to work well unlike other attempts):
 
-Warning
+<root>
-=======
+  bionic
+    dists
+      pgadmin4
+        InRelease
+        main
+          binary-all
+            Packages
+            Packages.gz
+            pgadmin4_4.21_all.deb
+            pgadmin4-web_4.21_all.deb
+          binary-amd64
+            Packages
+            Packages.gz
+            pgadmin4-desktop_4.21_amd64.deb
+            pgadmin4-server_4.21_amd64.deb
+          binary-i386
+            Packages
+            Packages.gz
+        Release
+        Release.gpg
+        Release.gz
+  buster
+  disco
+  eoan
+  focal
+  README
+  stretch
+  xenial
 
-These scripts are experimental - use at your own risk!
+Note that only the first branches are shown above; other branches (e.g. for
+buster, disco etc. follow the structure shown for bionic.
+
+Technically there are actually multiple repos here, one for each OS release.
+Note also that the binary-i386 directories do not contain any packages as we're
+not building 32bit packages for Linux. The directories and package indexes are
+present though, to prevent warnings being emitted on amd64 machines which are
+configured to support 32bit packages as well.
+
+In order to sign the repositories you need to import your signing private key
+into the gnupg2 keystore, for example:
+
+gpg --import signing_key.priv
+
+Once the files are in the right structure, we need to run a number of commands
+to generate the metadata, and sign the relevant files using GPG (in APT, we
+sign the repository indexes rather than the packages themselves.
+
+To create the metadata, first we create a config file for the apt-ftparchive
+program in $HOME/aptftp.conf (without the start/end markers):
+
+----------
+APT::FTPArchive::Release {
+  Origin "pgAdmin Development Team";
+  Label "pgAdmin 4";
+  Suite "pgadmin4";
+  Architectures "amd64 all";
+  Components "main";
+  Description "pgAdmin 4 - Development Tools for PostgreSQL";
+};
+Default {
+	Packages::Compress ". gzip bzip2";
+	Sources::Compress ". gzip bzip2";
+	Contents::Compress ". gzip bzip2";
+};
+----------
+
+Next, we create the package indexes. Run the following command for each OS
+release to be included (in the example, we're using bionic):
+
+for ARCH in all amd64 i386; do cd <root>/bionic && apt-ftparchive packages -c=$HOME/aptftp.conf dists/pgadmin4/main/binary-${ARCH}  > dists/pgadmin4/main/binary-${ARCH}/Packages && gzip -k dists/pgadmin4/main/binary-${ARCH}/Packages; done
+
+Now we need to create the release file for each OS release (again, using bionic
+in the example:
+
+cd <root>/bionic/dists/pgadmin4 && apt-ftparchive release -c=$HOME/aptftp.conf . > Release && gzip -k Release
+
+Finally, we can sign the release files. Replace <key name> with the email
+address on your signing key:
+
+cd <root>/bionic/dists/pgadmin4 && gpg -u <key name> -bao Release.gpg Release
+cd <root>/bionic/dists/pgadmin4 && gpg -u <key name> --clear-sign --output InRelease Release
+
+Note that it is important to run each command in the correct directory (hence
+the cd commands) to ensure the relative paths are created correctly in the
+indexes.
+
+Repository Configuration
+========================
+
+pgAdmin repo configurations live in /etc/apt/sources.list.d/pgadmin4.list. The
+file can be created with a command such as:
+
+sudo sh -c 'echo "deb https://server.company.com/apt/$(lsb_release -cs) pgadmin4 main" > /etc/apt/sources.list.d/pgadmin4.list && apt update'
+
+Assuming that <root> in the repository structure corresponds to
+https://server.company.com/apt/ from the client's perspective.
+
+If you have signed the repository, you'll also need to import the key on the
+client. This is done as follows for the pgAdmin signing key; adjust the URL as
+needed for your own:
+
+curl http://www.pgadmin.org/static/packages_pgadmin_org.pub | sudo apt-key add