Adds update procedure for opm-common keywords

Documents the procedure for updating the generated C++ code for Eclipse keywords from JSON definition files in the opm-common library.

This procedure is necessary when updating to a newer version of opm-common, when new keywords are added, or when existing keyword definitions change.

ThirdParty/custom-opm-common/CMakeLists.txt

@@ -39,6 +39,8 @@ set(OPM_ENABLE_DUNE false)
 set(BUILD_EXAMPLES false)
 
 if(CREATE_OPM_COMMON_KEYWORDS)
+  # See update-procedure.md for details about how to update the opm-common
+  #
   # In ResInsight, we need a subset of the files in opm-common. We also need to
   # generate the keywords. The flag CREATE_OPM_COMMON_KEYWORDS is set in the
   # main CMakeLists.txt file. When this flag is set, the opm-common is added to

ThirdParty/custom-opm-common/update-procedure.md

@@ -0,0 +1,52 @@
+# OPM-Common Update Procedure
+
+## CREATE_OPM_COMMON_KEYWORDS
+
+The `CREATE_OPM_COMMON_KEYWORDS` flag is a CMake option used to regenerate C++ code for Eclipse keywords from JSON definition files in the opm-common library.
+
+### Purpose
+
+ResInsight uses a subset of the opm-common library for parsing Eclipse simulation files. The Eclipse keywords are defined in JSON files within opm-common, and C++ parser code is generated from these definitions using the `genkw` tool.
+
+### When to Use
+
+Set `CREATE_OPM_COMMON_KEYWORDS=ON` when:
+- Updating to a newer version of opm-common
+- New Eclipse keywords have been added to opm-common JSON files
+- Existing keyword definitions have changed
+
+### Procedure in opm-common fork
+
+- ResInsight uses a fork of opm-common located at https://github.com/CeetronSolutions/opm-common
+- Current branch used by ResInsight is https://github.com/CeetronSolutions/opm-common/tree/development-01 
+
+1. Checkout the desired branch from the forked repository, usually `master`
+
+2. Create a new branch for your changes, e.g., `development-02`
+
+3. Apply clang-format on the following files EGrid, EInit, ERst, both header and cpp
+
+4. Cherry-pick commits from the previous used branch
+
+### Procedure in ResInsight main repository
+
+1. **Enable the flag**: Set `CREATE_OPM_COMMON_KEYWORDS=ON` in the main CMakeLists.txt (line 536). Configure the project using CMake to apply the change.
+
+2. **Build the solution**: When this flag is enabled, opm-common is added to the build solution and the keyword generation tools are compiled
+
+3. **Generate keywords**: Build a test target (e.g., CarfinTest.exe) to trigger C++ code generation using the `genkw` tool. The test target does no compile completely, but the generation step will complete successfully.
+
+4. **Copy generated files**: From the build directory `build/ThirdParty/custom-opm-common/opm-common/`, copy:
+   - `ParserInit.cpp` and `config.h` to `ThirdParty/custom-opm-common/generated-opm-common/`
+   - The entire `ParserKeywords/` folder to `ThirdParty/custom-opm-common/generated-opm-common/`
+   - The entire `include/` folder to `ThirdParty/custom-opm-common/generated-opm-common/`
+
+5. **Disable the flag**: Set `CREATE_OPM_COMMON_KEYWORDS=OFF` to return to normal build mode
+
+6. **Rebuild**: When disabled, the build uses the pre-generated files from `generated-opm-common/` instead of including the full opm-common build
+
+### Important Notes
+
+- When changing this flag, you must reopen the Visual Studio project
+- The flag is normally set to `OFF` to avoid the overhead of building opm-common during regular development
+- The generated files in `generated-opm-common/` should be committed to the repository after updates