- leave /guides/upgrade as symlink

upgrade/v1806-User-Upgrade-Guide.md

+<!-- --- title: User Upgrade Guide (OpenFOAM-v1806) -->
+
+[![home](/icons/home.svg "wiki home")](/home)
+[![upgrade](/icons/chevrons-up.svg "upgrade guide")][upgrade-guide]
+[![code](/icons/code.svg "coding patterns")][code-patterns]
+
+[[_TOC_]]
+
+## Environment
+
+Since OpenFOAM-v1612, `FOAM_INST_DIR` and `foamInstDir` no longer have any
+special meanings when sourcing the `bashrc` or `cshrc` files.
+
+The outdated use of `foamInstDir` and `FOAM_INST_DIR` has been largely removed.
+If you have environments that used these values, they may require
+adjustment.
+
+
+## Input dictionaries
+
+### system/controlDict
+
+Write compression value now takes a boolean value instead of the values `compressed` or `uncompressed`
+```
+writeCompression off;
+```
+
+## Moving mesh solvers
+
+Functionality from many moving mesh solvers promoted to their static mesh equivalents - see [v1806 release notes](https://www.openfoam.com/releases/openfoam-v1806/)
+
+## Meshing
+
+snappyHexMesh: correction to the layer feature angle controls - see [v1806 release notes](https://www.openfoam.com/releases/openfoam-v1806/)
+
+
+[code-patterns]: /coding/patterns/patterns
+[upgrade-guide]: /upgrade/upgrade
+
+[v1806-notes]: https://www.openfoam.com/releases/openfoam-v1806/