add basic explanation of how to add

Author: martenson

README.md

@@ -1 +1,16 @@
 # CESNET Galaxies Tool Management
+
+## to install a repo
+
+Create an entry in `GALAXY_URL/section_ID.yml` and open a PR.
+
+For `galaxy-umsa.grid.cesnet.cz/matchms.yml` it'd look like this:
+
+```
+tool_panel_section_label: matchms
+tools:
+- name: matchms_subsetting
+  owner: recetox
+- name: matchms_metadata_merge
+  owner: recetox
+```