Re-add adopters to docs, as an include

This is better than the symlink approach, because it allows the file
to live in its "canonical" place in the repository, while also avoiding
duplication when including the adopters in the docs. In fact, this opens
up more fine-grained control over how they are included, if this should
that become necessary in the future.

Signed-off-by: Tom Wieczorek <[email protected]>

docs/adopters.md

@@ -0,0 +1 @@
+{% include-markdown "../ADOPTERS.md" %}