[metacity] build: document library version change process

[Alberts Muktupāvels <muktupavels src gnome org>]

commit e95c3e981ade00233850f9ba36a7f250e2734a2e
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Mon May 4 22:36:30 2020 +0300

    build: document library version change process

 configure.ac | 11 +++++++++++
 1 file changed, 11 insertions(+)
---
diff --git a/configure.ac b/configure.ac
index f4949b64..e09b938d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -115,6 +115,17 @@ dnl **************************************************************************
 dnl Library version information
 dnl **************************************************************************
 
+dnl Before making a release, the library version should be modified. Follow
+dnl these instructions sequentially:
+dnl 1. If the library source code has changed at all since the last update,
+dnl    then increment lt_revision.
+dnl 2. If any interfaces have been added, removed, or changed since the last
+dnl    update, increment lt_current, and set lt_revision to 0.
+dnl 3. If any interfaces have been added since the last public release, then
+dnl    increment lt_age.
+dnl 4. If any interfaces have been removed or changed since the last public
+dnl    release, then set lt_age to 0.
+
 m4_define([lt_current], [3])
 m4_define([lt_revision], [0])
 m4_define([lt_age], [0])