[gimp] devel-docs: add OS support specific information.

[Jehan Pagès <jehanp src gnome org>]

commit 7409c98893b5b387ae11bb56e06e2d7a3d24bcaf
Author: Jehan <jehan girinstud io>
Date:   Mon Mar 26 23:32:38 2018 +0200

    devel-docs: add OS support specific information.
    
    I create this file so that we can refer to it to know whether we can use
    a OS-specific API, or if we want to know if we can safely bump a
    dependency, etc.

 devel-docs/os-support.txt |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)
---
diff --git a/devel-docs/os-support.txt b/devel-docs/os-support.txt
new file mode 100644
index 0000000..8105747
--- /dev/null
+++ b/devel-docs/os-support.txt
@@ -0,0 +1,20 @@
+## GIMP's Operating System Support
+
+GIMP is available on a wide range of operating systems.
+As a general rule, we should stop supporting a platform as soon as the
+publisher stops supporting it, or if it is nearly not used anymore.
+
+There is no accurate rule though, and it also mostly depends on what the
+developers maintaining GIMP for this platform will decide.
+
+### GNU/Linux, *BSD…
+
+Minimum dependency versions can be bumped if available in Debian Testing.
+
+### macOS
+
+Compatibility with 10.9 and over.
+
+### Windows
+
+Windows 7 and over.