[[ README ]] Document PR procedure

This patch adds notes about the required order of events when
patching this repo. Specifically it documents the different
procedures for updating the `develop-9.0` branch and the `develop`
branch.

Author: montegoulding

README.md

@@ -0,0 +1,39 @@
+# LiveCode Thirdparty Libraries
+
+The procedure for updating `thirdparty` on `develop-9.0` and `develop` branches is
+slightly different due to `thirdparty` prebuilts on develop. 
+
+## Update procedure for develop-9.0
+
+1. Push up a PR to this repo
+2. If there is a related patch to another repos then push up a PR for those
+3. Create a test branch on `livecode` with updated submodule ptrs. Ensure the
+branch is pushed upstream rather than to your clone.
+4. If it was a CEF update then push up a branch to `livecode-private` again with 
+updated submodule and kick off prebuilts on vulcan.
+5. Create a PR with the title beginning with `[[ NO MERGE ]]` and review it ok
+to confirm it passes on travis and vulcan
+6. Close PR from 5 and link to it in the other related PRs
+7. Once all related PRs are reviewed merge `thirdparty`, update submodules in
+`livecode` and merge any related PRs
+
+## Update procedure for develop
+
+The same procedure applies to merge-ups from `develop-9.0` because the 
+`thirdparty` prebuilts must be rebuilt for the current head of the `develop`
+branch.
+
+1. Push up a PR to this repo
+2. If there is a related patch to another repos then push up a PR for those
+3. Review and merge the PR for `thirdparty` but *do not* update submodule ptrs
+in `livecode` yet.
+4. Create a test branch on `livecode` with updated submodule ptrs. Ensure the
+branch is pushed upstream rather than to your clone.
+5. Push up a branch to `livecode-private` again with updated submodule and kick
+off prebuilts on vulcan.
+6. Once prebuilts are built for the `develop` head of `thirdparty` create a PR
+using the `livecode` branch with the title beginning with `[[ NO MERGE ]]` and
+review it ok to confirm it passes on travis and vulcan
+7. Close PR from 6 and link to it in the other related PRs
+8. Once all related PRs are reviewed, update submodules in `livecode` and merge
+any related PRs