Add a pointer from the doc sources to the online one

diff --git a/docs/README.md b/docs/README.md
new file mode 100644 (file)
index 0000000..58e7d51
--- /dev/null
+++ b/docs/README.md
@@ -0,0 +1,4 @@
+If you are browsing these files in the source archive, your probably
+want to read the online documentation: https://simgrid.org/doc/latest/
+
+This directory only contains the source files to build the documentation.
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