Prepare to generate r3.6.0-rc0 release documentation

Author: Clyde Bazile

README.md

@@ -31,6 +31,7 @@ Currently, no drivers guarantee API or ABI stability.
 | Family/version       | Stability   | Development         | Purpose                             |
 | -------------------- | ----------- | ------------------- | ----------------------------------- |
 | (repo master branch) | Unstable    | Active development  | New feature development             |
+| mongocxx 3.6.x       | Unstable    | Bug fixes only      | Upcoming stable C++ driver release  |
 | mongocxx 3.5.x       | Stable      | Bug fixes only      | Current stable C++ driver release   |
 | mongocxx 3.4.x       | Stable      | None                | Previous stable C++ driver release  |
 | mongocxx 3.3.x       | Stable      | None                | Previous stable C++ driver release  |

docs/content/mongocxx-v3/installation.md

@@ -32,6 +32,7 @@ have problems, please file a bug report via
 
 The mongocxx driver builds on top of the MongoDB C driver.
 
+* For mongocxx-3.6.x, libmongoc 1.17.0 or later is required.
 * For mongocxx-3.5.x, libmongoc 1.15.0 or later is required.
 * For mongocxx-3.4.x, libmongoc 1.13.0 or later is required.
 * For mongocxx-3.3.x, libmongoc 1.10.1 or later is required.