Add instructions on how to compile a forked repo.

Author: Tom Verbeure

README.md

@@ -20,6 +20,46 @@ Refer to the "getting started" chapter of the User manual
 
 * [User manual Compilation (HTML)](https://www.ngscopeclient.org/manual/GettingStarted.html#compilation)
 
+## Compiling a forked repo
+
+If you want to contribute changes to scopehal-apps, you should make them in a
+forked repo so that you can create pull request with your changes.
+
+Following these steps:
+
+* Fork a bunch of GitHub repos to your own GitHub account
+
+  Right now, the build system requires that your GitHub account has cloned version of the
+  VkFFT, xptools and logtools. It's best to clone the version that under the ngscopeclient
+  account, this ensure that you're working with the same version as the core development
+  team.
+
+  * [ngscopeclient/VkFFT](https://github.com/ngscopeclient/VkFFT)
+  * [ngscopeclient/xptools](https://github.com/ngscopeclient/xptools)
+  * [ngscopeclient/logtools](https://github.com/ngscopeclient/logtools)
+
+* Fork the `scopehal-apps` repo (this one!)  to your own account
+* Clone your personal repo to your development machine
+
+  `git clone --recursive git@github.com:<your github username>/scopehal-apps.git scopehal-apps`
+
+* Follow the regular compilation instructions.
+
+  If you want to create executables with debug symbols, make sure to change option `MAKE_BUILD_TYPE`
+  from `Release` to `Debug` when running `cmake`.
+
+  It is possible that `cmake` errors out with the following error messages:
+
+  ```
+CMake Error at CMakeLists.txt:82 (message):
+  Unrecognized version tag 53152c7c / 53152c7c, can't create a VERSIONINFO
+  from it.  Must be of format v1.2, v1.2.3, v1.2-rc3, v1.2.3-rc4
+  ```
+
+  You can fix this by creating a dummy tag in your local repo:
+
+  `git tag v0.0.0`
+
 ## Special comments
 
 The following standard comments are used throughout the code to indicate things that could use attention, but are