Add the REQUIREMENTS docs.

README.rst

@@ -482,7 +482,24 @@ connection to the client is closed.
 REQUIREMENTS
 ============
 
-The VFP requires Varnish version XXX ...
+The VFP currently requires the Varnish master branch.
+
+The VFP also requires the `Google brotli library`_, which is installed
+as separate libraries for compression and decompression,
+``libbrotlienc.so`` and ``libbrotlidec.so``. These in turn depend on a
+third library ``libbrotlicommon.so``. Package managers for most
+distributions provide these under names like ``libbrotli`` or
+``libbrotli1`` (and the package manager takes care of the dependencies
+for you). You can also build the library from source; see the
+repository address shown below.
+
+The VFP has been tested with version 1.0.5 of both the encoder and
+decoder libraries.
+
+If you are building the VFP from source, you will need development
+versions of the brotli libraries. See
+`CONTRIBUTING.rst <CONTRIBUTING.rst>`_ in the source directory
+for details.
 
 INSTALLATION
 ============

src/vfp_brotli.vcc

@@ -446,7 +446,24 @@ connection to the client is closed.
 REQUIREMENTS
 ============
 
-The VFP requires Varnish version XXX ...
+The VFP currently requires the Varnish master branch.
+
+The VFP also requires the `Google brotli library`_, which is installed
+as separate libraries for compression and decompression,
+``libbrotlienc.so`` and ``libbrotlidec.so``. These in turn depend on a
+third library ``libbrotlicommon.so``. Package managers for most
+distributions provide these under names like ``libbrotli`` or
+``libbrotli1`` (and the package manager takes care of the dependencies
+for you). You can also build the library from source; see the
+repository address shown below.
+
+The VFP has been tested with version 1.0.5 of both the encoder and
+decoder libraries.
+
+If you are building the VFP from source, you will need development
+versions of the brotli libraries. See
+`CONTRIBUTING.rst <CONTRIBUTING.rst>`_ in the source directory
+for details.
 
 INSTALLATION
 ============