[gnome-software: 3/4] docs: Add pointers to general app developer/vendor docs in README

[Philip Withnall <pwithnall src gnome org>]

commit 8c20e34b3722233785bfd97846a4d0a44a5931fd
Author: Philip Withnall <pwithnall endlessos org>
Date:   Fri Mar 4 14:40:43 2022 +0000

    docs: Add pointers to general app developer/vendor docs in README
    
    Rather than including specific documentation about `--show-metainfo`,
    which is already documented in `doc/app-developers.md`, give some
    pointers to the documentation in `doc/`.
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>

 README.md | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)
---
diff --git a/README.md b/README.md
index 4c40f86bf..077b0ab7c 100644
--- a/README.md
+++ b/README.md
@@ -31,14 +31,13 @@ Bug reports and merge requests should be filed on [GNOME GitLab](https://gitlab.
 
 For development discussion, join us on `#gnome-software` on 
[irc.gnome.org](https://wiki.gnome.org/Community/GettingInTouch/IRC).
 
-# Testing a metainfo/appdata file of an application
+# Documentation for app developers and vendors
 
-If you are developing an application, and want to see how your under-development
-metainfo file will appear when it’s eventually published into GNOME Software,
-run:
-```
-$ gnome-software --show-metainfo=./path/to/your/org.example.App.appdata.xml.in
-```
+Specific documentation is available for application developers who wish to test
+how their applications appear in GNOME Software; and for distribution vendors
+who wish to customise how GNOME Software appears in their distribution:
+ * [Tools in GNOME Software for application developers](./doc/app-developers.md)
+ * [Vendor customisation of GNOME Software](./doc/vendor-customisation.md)
 
 # Running a nightly build